Brightwood native Robert White defeated long-time D.C. Council member Vincent Orange in the Democratic primary for an at-large seat. He's on the Kennedy Street corridor, one of the struggling commercial strips he'd like to see revitalized. (Fenit Nirappil/The Washington Post)

Political neophyte Robert White had a plan: Take on a well-known D.C. politician, clear the field of spoilers and appeal to new residents flooding into the District.

It worked.

In the biggest upset of Tuesday’s Democratic primaries, White, 34, defeated 12-year-incumbent Vincent B. Orange, 59, in the race for an at-large seat on the D.C. Council. The victory established White as a giant-slayer and — as the Democratic nominee in November — a likely fresh new face on a legislative body that grows increasingly younger and more progressive.

Orange had never lost a race as an incumbent in 11 campaigns since 1990, and he entered the latest election with a fundraising edge and a notable legislative achievement: He negotiated a deal for a $15 minimum wage that drew national attention.

Sheer longevity and name recognition had always given him an edge in crowded fields, despite being seen as vulnerable because he barely held on to his seat in 2012 and his reputation was marred by a recent ethics charge.

The third candidate in Tuesday’s race, newcomer David Garber, attacked Orange for ethics failures and used mailings that included a large image of a rat.

Political observers attribute the upset to a mix of Orange’s unpopularity, White’s persistent and focused campaign, and an anti-incumbent wave that felled three of four incumbents.

“Vincent Orange was never a super-popular elected official,” said Michael Fauntroy, an associate professor of political science at Howard University. “When presented with a viable alternative, the voters took it.”

White’s victory means that in just two years, voters will have replaced a majority of the 13-member council, usually with political novices, and, often, ousting long-serving incumbents.

White, a former aide to D.C. Del. Eleanor Holmes Norton (D), lost his first race, in 2014, for an open at-large seat.

Soon after that loss, he was hired by newly elected Attorney General Karl A. Racine as director of community outreach, boosting his visibility for nearly a year before he decided to take on Orange.

Heeding the lessons of his failed 2014 bid, White hired the same consultants who ran Racine’s campaign. He worked to clear the field of potential spoiler candidates, though Garber stayed in and drew 15 percent of the vote.

White had pledged to increase oversight of city agencies and address the displacement of people priced out of their homes. He supports a legislative proposal to require employers in the District to provide 12 weeks of paid sick leave.

He was endorsed by council member Mary M. Cheh (D-Ward 3), tenants rights groups, the Gay and Lesbian Activists Alliance, a Latino caucus, and other progressive organizations. He also received support from former mayor Vincent C. Gray and Trayon White as they campaigned for council seats east of the Anacostia River, a stronghold for Orange.

“We started out with a much greater aim: We were going to work the city, not just some wards,” said Sean Rankin, White’s campaign manager.

White won his largest number of votes in Ward 3, in the city’s affluent upper Northwest, where voters turned out at the highest rate in the city, even though the only competitive contest for those voters was the at-large seat.

He prevailed in a block — Wards 1, 2 and 6 — stretching from Georgetown to Capitol Hill, which have all seen increasing property values and an influx of younger voters in the last five years.

White cut into Orange’s usual base of support, drawing 36 percent of the vote in Orange’s home Ward 5. And he pulled in more than a quarter of the vote in Wards 7 and 8, where low turnout also depressed Orange’s vote haul.

“Certainly, I think Robert caught fire with younger voters – part of his appeal is his relative youth and his awareness of both D.C.’s — the old D.C. and the newly developing District of Columbia,” Racine said. “Robert is one who can serve as a bridge between those two.”

On the campaign trail, White had also aggressively attacked Orange, accusing him of pay-to-play politics and dismissing his ideas as outlandish, including Orange’s plan to address the housing crunch with 1,000 tiny homes for millennials and seniors.

For this campaign, Orange retired some of his past campaign gimmicks — like giving away oranges while riding a Segway — and presented himself as a more serious candidate. He tried to highlight his work on the minimum wage and other labor achievements.

“It’s very difficult to make a second first impression, and the first impression to Vincent Orange was that he was a bit of a clown,” said Chuck Thies, a campaign aide to Gray, who considered taking on Orange.

“A lot of voters were suffering from what I call ‘Orange fatigue,’ ” said Dorothy Brizill, a longtime city activist and election monitor. “Every time you turned around, he was on the ballot.”

Rosa Lee, a 68-year-old retiree in Brightwood Park, voted for White because she thought the longtime council member was getting too combative, too stale and too odd.

“He reminds me of the late Marion Barry on some facets, and I am interested in bringing in new perspectives,” Lee said.

On Wednesday, Orange said he wouldn’t rule out trying to keep his seat by running as an independent in November’s general election, but he acknowledged that White was likely to take his seat. “It’s time for the city to get behind the new leadership,” Orange said. “Who knows — my public service may continue, but right now, it looks like it’s going to be paused.”

In an interview Wednesday, White said he’s not going to take the November election for granted, although he’ll need to take a campaign pause for his first child, due in three weeks.

He also insisted that he wouldn’t be a puppet of Racine, who has clashed with Mayor Muriel E. Bowser, or at loggerheads with the mayor. “I don’t know that I have an ideology,” said White. “I’m very focused on outcomes — really not so much labels that come up with other people’s baggage.”

Aaron Davis contributed to this report.