When Larry Summers asked Sheryl Sandberg, his up-and-coming special assistant at the Treasury Department, who else he should hire, she didn’t hesitate. David Fischer was the best of the young staffers at the department, she said. That was in 1998. Since then Fischer has followed closely in the footsteps of his champion. After earning an MBA at Stanford, he became Sandberg’s top deputy at Google, helping build a 4,000-employee ad operations group. When she left to become Facebook’s COO, he first assumed her duties at Google and then joined her at Facebook in 2010. As vice president of business and marketing partnerships, the soft-spoken executive helped turn a nascent ad business into a $5 billion juggernaut. “He is incredibly efficient, and he is always the calmest person in the room,” Sandberg tells Fortune.
At Facebook, Fischer, 40, quickly won plaudits for his thoughtfulness — and for eschewing the irksome, we-know-better attitude adopted by some ex-Googlers. “Before he even started, he came in to schedule extensive meetings,” says one of Facebook’s earliest ad executives. “He really wanted to develop a deep understanding of our business.”
Fischer has faced plenty of skeptics as he’s worked to court major advertisers. But his group’s ability to devise effective campaigns for the likes of American Express and to develop tools for advertisers to measure results has won Facebook an ever-growing number of converts. And over the past year, Fischer has begun persuading them to try the social network’s mobile ads. The results speak for themselves: In the fourth quarter of 2012, 23% of Facebook’s $1.3 billion in ad revenue came from mobile, up from zilch the year before. While there is plenty of room to improve mobile-ad products, he says, “it gives us confidence that we have created a mobile-ad business that is compelling.”
For all his successes, Fischer, who started his career as a reporter for U.S. News & World Report, still finds himself in the hot seat when a major marketer grumbles about the effectiveness of a campaign, or worse, decides to bail on the social network altogether, as GM did very publicly last year. The seemingly unflappable Fischer takes it in stride. “I am completely confident in the efficacy of our ads,” he says. It took marketers more than a dozen years to warm up to television advertising, he adds. The social network is just nine years old. Its ad business is younger still. At Facebook’s size, it’s only natural that some campaigns will flop. “The fact that might happen sometimes is no more damning for us than it is for print or TV or any other form of advertising,” Fischer says. Perhaps. But getting advertisers to see things that way may prove to be his most enduring challenge.
This story is from the March 18, 2013 issue of Fortune.