In November 2016, Facebook CEO Mark Zuckerberg and COO Sheryl Sandberg were heads down in a war room navigating the fallout of social media’s role as an amplifier of far-right misinformation that helped elect U.S. President Donald Trump. Around the same time, Nicola Mendelsohn, then Facebook’s vice president of Europe, Middle East, and Africa (EMEA), was sitting at home in London with her husband, living through the worst weekend of her life. Her American colleagues’ political problems were likely very far from her mind.

Mendelsohn had discovered an unusual lump near her groin. She didn’t think anything of it, but a doctor suggested she get a scan. That Friday, she put her phone down and came back to see missed call after missed call from her doctor. She knew the news couldn’t be good. She spiraled, imagining the very worst, thinking about what she would tell her four kids. “I felt a physical feeling that this is really bad—like you’ve been hit in the solar plexus,” she remembers.

The results were as bad as she feared: The small lump was one of several tumors all over her body. She had follicular lymphoma, an incurable blood cancer that 25,000 Americans are diagnosed with each year.

That was almost seven years ago. After that horrible weekend, Mendelsohn vowed never to feel that hopeless again. Her doctor first monitored her cancer’s progression, then she began treatment that continued until the pandemic, when Mendelsohn isolated at home because of her weakened immune system. Now, at age 51, she has no evidence of disease, and advocates for patients with the under-researched and underfunded illness.

A cancer diagnosis can be a clarifying experience that prompts patients to reorder their lives. Work can become an afterthought. Mendelsohn also had that moment of clarity, except her diagnosis reinforced that she wanted to keep things as they were. She loved her life; her ad savvy aligned with Facebook’s purported mission to connect the world—a cause she deeply believes in. Her theater-kid energy had endeared her to colleagues and London’s creative community. “People want Nicola to win,” says Michael Kassan, the well-connected CEO of MediaLink, a strategic advisory firm.

Throughout the ordeal, Mendelsohn kept working and continued to climb the ranks at Facebook, and now Meta. This February, Meta promoted Mendelsohn to head of its global business group, an influential job handling relationships with the large advertisers that contributed the bulk of Meta’s $114 billion in ad revenue last year. She also oversees its business partnership network and global business engineering team. With the departures of executives like Sandberg and Marne Levine, Mendelsohn, who reports to COO Javier Olivan, has become one of the most senior women at the global tech giant.

The promotion is a career feat for the Manchester, England, native who never set out to be a high-powered executive. But Meta’s current state has tinged the achievement: Over the past year, it recorded three straight quarters of declining year-over-year sales, and it has announced layoffs of roughly 24% of its workers. It faces a dim economic outlook for advertisers whose dollars fuel Meta’s sprawling machine.

Mendelsohn doesn’t pretend that her experience with cancer inspired any life-altering changes. Rather, it cemented her existing management style: to distill the task at hand into smaller, manageable pieces; the big picture can be too overwhelming. That’s how she survived the acute phase of her diagnosis; that’s how she plans to navigate her piece of Meta’s larger, existential crisis.

Like many Meta executives, Mendelsohn can talk a lot without saying much. Except when Mendelsohn does it, the effect can be genuinely charming. The relatively new New York City resident is sitting in the Instagram section of Meta’s hip Astor Place offices. She arrives with her usual bubbly greeting—a hug—and her signature feminine style, her nails painted a chrome purple.

When asked about metrics for Facebook’s relatively new Instagram Reels, the short video posts that offer fewer opportunities for ads than Instagram Stories and Facebook’s feed, she says messaging is the future and launches into a story about shopping for shoes in Brazil via Meta’s WhatsApp service. She uses an anecdote about growing up in England with one television set to deflect a question about the privacy concerns around targeted advertising. “I had to watch a lot of ads that had nothing to do with me,” she recalls. She shares that her 25-year-old daughter is engaged. Now the ads she and her daughter see are for wedding paraphernalia. “Personalized advertising means I get to see things I’m interested in,” she says.

As the face of Meta to major global advertisers, Mendelsohn’s charisma has served her well. When advertisers have soured on Facebook—like during their 2020 boycott over hate speech and misinformation—they still seemed to like Mendelsohn. They appreciated her enthusiasm, her interest in their perspectives and concerns, and her personal flourishes, like her thoughtful gifts. She gave one newly promoted advertising exec a bracelet featuring an evil eye, meant to keep watch on her behalf.

Mendelsohn grew up as the eldest child and only daughter of observant Jewish parents. Her mom ran a catering business and her grandmother was a haberdasher—two early role models for working women. Mendelsohn wanted to be an actress, but observing the Sabbath made Friday night theater shows a nonstarter.

She left home to attend the University of Leeds, where she met Jonathan Mendelsohn, a former Labour Party political strategist who now holds a seat in the House of Lords, making his wife Lady Mendelsohn.

Mendelsohn was unsure of what to do after university and decided to explore London’s advertising industry. Her friendliness clashed with the city’s stoicism—her chitchat drew strange looks on the Tube—but served her well in the creative and relationship-heavy ad business. She climbed the ranks of Britain’s top ad agencies, from Bartle Bogle Hegarty, to Grey, to Karmarama, running campaigns for Cadbury, Polaroid, and Häagen-Dazs’s entry into the U.K.

She and Jonathan married young, and Mendelsohn gave birth to the first of her four children at 26. Unlike some of her peers at Fortune 500 companies, she never really aimed to be a CEO or even to have a big career. Instead, she “wanted to be a grandmother” and to have a job that she was interested in and enjoyed. She kept working but at times prioritized family, choosing a four-day-a-week schedule and a 20% pay cut for years—until she heard from Carolyn Everson, a Facebook exec in a role similar to Mendelsohn’s today.

In 2013, Facebook needed someone to head its EMEA business, which was still nascent with less than $2 billion in revenue. Mendelsohn wasn’t an obvious choice; she’d never worked for a major global business or a tech company. But Mendelsohn was a consummate networker who made friends easily in Britain’s tight-knit advertising community. Plus, as president of Britain’s Institute of Practitioners in Advertising, she had championed digital advertising early. So she interviewed for the Facebook job, got it, and made the jump from four days a week to five, from British advertising to global technology.

Charts show Meta stock price and quarterly revenues

In her eight years as vice president of EMEA, Mendelsohn oversaw 1,500% revenue growth to almost $28 billion annually. (Facebook recorded 1,700% growth in the same period.) She opened new offices and set up business operations in Norway, Israel, and South Africa. Mendelsohn centralized various “Africa” initiatives, from broadband access to user growth, to launch Facebook’s first office on the continent; in Israel, she capitalized on the startup culture to build products for small companies.

Along the way, Mendelsohn earned the respect of her bosses and her more technical colleagues. In addition to maintaining relationships with advertisers, she liaised between those customers and Facebook engineering teams, suggesting new features and products. “She understands our products. She understands the metrics. She understands what advertisers are looking for. But she also understands people and what makes them click,” says Sandberg, Mendelsohn’s former boss and Meta’s COO until she stepped down last August.

Mendelsohn, shown here with Meta chief product officer Chris Cox and Meta global affairs president Nick Clegg at the 2023 World Economic Forum, is a consummate networker who endeared herself to London’s creative community.

Mendelsohn became indispensable, weighing in on matters beyond her purview; while the 2020 advertiser boycott was a U.S. issue, her industry expertise from Europe made her a critical strategist in Facebook’s response. Nick Clegg, the U.K. deputy prime minister turned Facebook president of global affairs, remembers Mendelsohn’s ability to distinguish between general media uproar over Facebook’s role in politics and the key issues that advertisers wanted addressed, like their content appearing next to hate speech. “Some people might get into a tailspin. Others just shrug their shoulders,” Clegg says. “[She could] see wood for the trees.”

Only three years into her tenure at Facebook in 2016, Mendelsohn had made a name for herself. So when she received her diagnosis, she had allies in her corner.

Mendelsohn’s “legendary energy,” as Clegg describes it, hasn’t faltered throughout our conversation at Meta’s NYC office. Until we get to a big topic: her cancer. Mendelsohn’s voice drops into a lower register; she gets quieter and sits back in her chair.

She’s told the story of her diagnosis before—to her bosses, to her employees, to supporters of the Follicular Lymphoma Foundation she started. But remembering the first time she told her four children gives her pause. She rests her head in her hands.

A week after Mendelsohn’s diagnosis, she and Jonathan sat the kids down around their dining room table in London. Her oldest child and only daughter, Gabi, was 20; her youngest son, Zac, was 11. “He was so little,” Mendelsohn remembers, her voice wavering. They had waited a week to figure out all the facts and so as not to ruin an elder son’s birthday party.

They told the kids that their mom had cancer. “I couldn’t get the words out,” Mendelsohn remembers. “Everything was happening in slow motion.” They couldn’t comfort the family by saying she would start treatment right away; her doctors recommended treating the cancer only when it progresses to a certain point. Zac asked if their mom was going to die.

The question was impossible to answer. Follicular lymphoma is considered incurable. No chemotherapy can ever guarantee that the cancer is entirely gone. Half of patients diagnosed make it five years; one-third live another 15 years.

After its initial slow progression, the disease “takes off” in the lymph nodes and bone marrow, explains Dr. Jonathan Simons, an oncologist and former professor of hematology who helped Mendelsohn establish the Follicular Lymphoma Foundation. For 18 months, Mendelsohn’s diagnosis was a fact of life as she and her family waited for doctors’ go-ahead to start treatment. She couldn’t do anything besides improve her diet and start exercising (boxing, walking, dancing).

After she began chemotherapy, Mendelsohn didn’t have the stereotypical experience. Her long, thick hair thinned, but she never had to wear the wig she bought in anticipation of losing all of it. And she didn’t take time off work. She says she never considered it even as Facebook endured the public’s wrath. She brought her laptop to treatment sessions and conducted meetings virtually. (She’s cofounded a pledge to support workers battling cancer with Publicis CEO Arthur Sadoun.) She was determined to maintain the life she’d built—at home and at work—despite the diagnosis: “Still married to the same guy, same job,” she jokes.

The pandemic cut short the final stage of her treatment—immunotherapy. She isolated in her London home, including from her youngest son when he went back to school. Her low B-cell count meant that COVID vaccines didn’t work on her. In April 2021 she received a drug that produced synthetic antibodies, allowing her to get back outside. Later that year she was promoted from VP of EMEA to VP of the global business group, a precursor to her current role, and moved to New York. She’s had no evidence of the cancer since 2018, but the nature of follicular lymphoma means the word “remission” doesn’t really apply.

Mendelsohn says her dedication to Facebook was less about furthering her career and more about advancing the company’s mission. For the ultimate people person, the possibilities that come with reaching 3 billion people each day were hard to give up. She’s a true believer in the good that can come from connecting people, a throwback to the earliest days of social media before the risks—fast-moving misinformation, the spread of hate speech—became clear. She finds meaning in supporting businesses, providing U.S. advertisers with $3.31 in revenue for every dollar they spend on Meta platform ads. “These are the kinds of numbers that get me and my team out of bed every day,” she told the press in May.

This year has tested even the most ardent Meta supporter. After a COVID-era boom, the global advertising market has contracted, and Meta’s revenue growth has slowed. In mid-2022, Meta reported a decline in year-over-year revenue for the first time since its 2012 IPO. The 1% year-over-year dip—accompanied by a 36% drop in profit—was a wake-up call. CEO Mark Zuckerberg declared 2023 the “year of efficiency.” Translation: layoffs. Meta has initiated at least four separate rounds of cuts since November, slashing more than 21,000 workers, about 24% of its workforce.

Meta also faces threats that will outlast the calendar year. Its platforms are losing relevance among younger generations enraptured by rival TikTok. More generally, users have grown distrustful of social media; content from influencers and brands—not friends—floods their feeds. It’s possible that the social part of the social media era—which Facebook pioneered—has peaked.

That heavy question is for Zuckerberg to ponder. Mendelsohn is chipping away at the smaller, operational challenges on her plate.

In May, Meta’s layoffs hit the business groups where Mendelsohn is a leader alongside Justin Osofsky, who oversees smaller businesses, online sales and operations, and partnerships. She’s responded to low worker morale (made worse by the cuts’ staggered rollout) by spinning the focus on efficiency as a return to the good old days of Facebook. “This is kind of getting us back to our roots, getting us back to being much more agile, much more nimble,” she says. Meta can now “create and innovate new products in new and faster ways than we’ve done before.”

“[Nicola] understands our products. She understands the metrics. She understands what advertisers are looking for. But she also understands people and what makes them click.”
Sheryl Sandberg, former COO, Meta

Outside Meta, the economic outlook is grim too. Worldwide digital ad spending is forecast to reach $601 billion this year, but the pace of growth is slowing, according to Insider Intelligence. Between Facebook and Instagram, Meta eats up 20% of advertisers’ digital budget. In a downturn, they want proof that that strategy is paying off. Executives at Meta’s regular Global Client Council meetings of 25 top advertisers—which Mendelsohn hosts—once focused on hate speech. Now they’re concerned about return on their investment. “Where do we spend our money? How do we spend our money most effectively? Is it Facebook, Instagram Reels, or TikTok?” asks Lindsay Pattison, chief client officer for the British advertising and communications firm WPP.

A 2020 privacy tweak by Apple has made that gloomy ad climate worse. That year, Apple sent iOS users a prompt that asked if they wanted to be tracked when using Facebook and other apps. Meta estimated that such policies would cost it $10 billion in revenue. It has automated more of the advertising experience, helping to offset the cost for advertisers. Still, Mendelsohn goes after Apple: “A number of different businesses have cited bankruptcy [because] they weren’t able to target their customers directly,” she says, citing a hypothetical small-town pizza shop. But the Apple changes “impacted our business as well,” she acknowledges.

Then there’s TikTok. If the ByteDance-owned app can figure out how to monetize at the same level as Meta, it will earn billions more each year. “Could that come at the expense of someone else?” asks Bernstein Research analyst Mark Shmulik. “You just can’t ignore it, because they’re not standing still over at TikTok.” Mendelsohn says she’s focused on increasing value for advertisers: “They’re coming where they can get the growth, and they get that from us.”

Meta is hardly ignoring TikTok, yet some of its efforts to compete with the app may be cannibalizing its own business. Videos posted on Reels, Meta’s answer to TikTok, are longer than Stories, which means fewer opportunities to play ads in between posts—and lower monetization. Yet Meta claims users are watching more Reels—140 billion plays a day across Instagram and Facebook—and spending less time on the feed, which cuts into ad revenue. Mendelsohn says Facebook saw the same pattern when it introduced Stories, which initially monetized at a lower level than static image posts. Instagram Reels’ monetization efficiency improved 30% last quarter, Zuckerberg said in Meta’s most recent earnings report.

140 billion
The number of Reel plays on Instagram and Facebook every day, according to Meta.

“[Meta is] in a pivotal moment—revenue growth has stalled. They’re not growing. They’re having massive cuts,” says Jefferies analyst Brent Thill. “They’re trying to experiment with new business models. But at the end of the day, the main engine is advertising, which is a really tough place right now given the economy.”

Mendelsohn says Zuckerberg’s new obsession—A.I.—can help solve those problems in small ways. The average Meta advertiser saw 20% higher conversions in the fourth quarter of 2022 mainly because of A.I., she says. In May, Meta announced the planned rollout of its “A.I. Sandbox” of tools: A.I. that adjusts brightness and text placement to increase ad performance, plus generative A.I. that writes copy and creates image backgrounds. Automating the nitty-gritty lets marketers spend more time on the skills that give them a “competitive advantage,” like developing campaigns and targeting the right users.

After months of disappointing earnings, Meta delivered good news in April. It reported 3% year-over-year sales growth, its first increase in almost a year and a sign it’s rebounding from the blow of Apple’s rule change and beginning to gain market share in short-form video.

Today, Mendelsohn’s cancer isn’t all-consuming. “Now I don’t think about it every day,” she says. “That’s something I never could have imagined when I was diagnosed.” What she does think about is finding a cure for follicular lymphoma, something she “absolutely” expects in her lifetime. A cure could be applied to other diseases that share follicular lymphoma’s DNA structure, like breast cancer. Simons calls Mendelsohn the “Michael J. Fox of follicular lymphoma.” The visibility—and money—a top Meta exec can bring to an under-resourced disease could change the lives of the 1.2 million people with this illness.

Still, a question looms: What if researchers don’t find a cure? Follicular lymphoma recurs in the average patient six to eight times, with increasing frequency. Mendelsohn is encouraged that her disease hasn’t returned for five years. Her young age at the time of her diagnosis makes her “not the typical follicular lymphoma patient,” which gives her hope that the other stats won’t apply either.

Mendelsohn’s upbeat outlook can at times feel at odds with the prospects in front of her. She’s not sure where the disposition comes from—“I’ve just always felt incredibly grateful, from being a child,” she says—but says it’s a by-product of focusing on what she can control, rather than “the very big thing.” That approach makes the challenges on her plate—whether living with cancer or the future of one of the world’s largest tech companies—a little easier to handle.

Today she flies around the world every week. She jetted between New York, Israel, Palo Alto, and King Charles III’s coronation in a one-month span this year. She set a goal to visit 100 countries, and crossed the 100th off her list with a holiday vacation to St. Lucia. And she remains as committed to the future of Meta as ever, metaverse included. “I can’t imagine being anywhere else,” she says. “I love Mark’s vision of where the next stage will get us to.”

“I’m getting on with my life,” Mendelsohn says. Online and off.

This article appears in the June/July 2023 issue of Fortune with the headline, “Meta’s true believer.”

Nicola Mendelsohn battled an incurable cancer on her way to becoming a top Meta exec. Now she’s trying to solve the Facebook parent’s growth crisis