Four years ago, Dylan Field was living in a one-bedroom apartment in San Francisco’s gritty Mission District, where he would stop for a $1 cup of coffee on his way to work.

The college dropout was anonymous – and shy – enough that at freewheeling networking events held by the city’s omnipresent venture-capital firms, Mr. Field would often stand alone, awkwardly nursing a drink.

On Thursday, his design-software company, Figma, agreed to be sold to rival Adobe Inc. for $20 billion, suddenly making Mr. Field, 30, one of the most talked-about people in the technology world.

The rise of Figma, which Mr. Field co-founded with a former Brown University classmate, was fast even by the standards of Silicon Valley. In early 2018, the company was valued privately at $115 million. By last year, in another fundraising round, that valuation had soared to $10 billion, a level doubled by Adobe’s deal. The rapid appreciation is noteworthy as prices for most technology companies, public and private, have been in free fall in recent months.

Mr. Field, according to investors and others who know him, still owns a sizable chunk of the company, along with venture-capital heavyweights including Sequoia Capital and Greylock Partners. If the deal closes, Mr. Field would be a billionaire.

Figma co-founder Dylan Field says he is still trying to process the scale of the changes to his life.

Photo: David Paul Morris/Bloomberg News

In an interview a few hours after the deal announcement, Mr. Field said he was still processing the scale of the changes to his life. While Adobe had approached him several months ago to begin talks, Mr. Field said the announcement was pushed forward after his team heard that The Wall Street Journal had begun making inquiries. He said he was awake for much of the night as they raced to get news of the deal out.

Despite that effort, market reaction to the deal was poor. Adobe’s shares fell nearly 17% on Thursday, suggesting widespread investor opposition to the acquisition. Mr. Field said he wasn’t fazed.

“If this deal fell apart tomorrow, I’d feel just fine,” he said.

Mr. Field grew up just north of San Francisco in Sonoma County, Calif., part of the area’s famed wine region. When he was around 3 years old, his family bought a computer, and Mr. Field taught himself—and his parents—how to use it, the family has said.

By his own account, Mr. Field was an unremarkable student, at risk of dropping out until he joined the robotics team and began taking college-level courses in high school. He was rejected by the University of California, Berkeley and enrolled instead at Brown.

During his junior year, Mr. Field applied for a fellowship run by the billionaire financier Peter Thiel. The fellowship, then not particularly well-known, offered applicants $100,000 in no-strings-attached funding if they agreed to drop out of college to pursue entrepreneurial aims.

He pitched new software to modify drones to monitor traffic and catch reckless drivers.

Mr. Field was accepted for the fellowship and left Brown. The drone company didn’t work, but his next idea, Figma, took off.

Started with

Evan Wallace, a friend of Mr. Field’s from Brown, Figma is a graphics-editing platform that allows people to design projects together. It took four years from inception to the company’s launch of a product—a period that didn’t always portend the success to come.

The Figma office was located above a busy bar, and on Fridays, starting around 3 p.m., the noise was unbearable, said Badrul Farooqi, an early employee.

The team wasn’t much for late nights, as Mr. Field is a “board games and wine type,” Mr. Farooqi said. The Figma CEO once told staff that he had hired an executive coach to help him work on his presence.

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Figma, like other software services, grew rapidly during the pandemic. Clients included Uber Technologies Inc. and Square Inc., now known as

Block Inc. Among Figma’s advantages: Its browser-based tools work simultaneously across various platforms, as opposed to competing products that operate only on a desktop or an app.

Late last year, Mr. Wallace departed the company. Mr. Field said his partner was burned out by the work and wanted to try new projects. Mr. Wallace couldn’t be reached for comment.

By this year, Mr. Field was a new father, and Figma was preparing for an initial public offering. That was until the IPO market froze up. Adobe’s offer was preferable to risking a public listing, Mr. Field said, even if some longtime fans of the product have expressed dismay that it will be absorbed by a traditional technology giant.

Mr. Field is still adjusting to the new status. Asked if he was now, in the Silicon Valley vernacular, a tech bro, he demurred.

“I don’t know,” he said. “You tell me.”

Write to Rob Copeland at rob.copeland@wsj.com