D.C. Council member Jack Evans, for three decades a powerful fixture of District government, said Tuesday that he will resign from office, allowing him to avoid being expelled by his colleagues for more than a dozen ethics violations.

The city’s longest-serving lawmaker, Evans (D-Ward 2) for months had rebuffed demands from council members, civic leaders and activists that he step down. But as the council was about to meet to offer him a last chance to defend himself, Evans told Chairman Phil Mendelson (D) that he would resign Jan. 17.

“I believe Washington, DC to be the pride of the nation and I am proud of the contributions I have made in helping to create a vibrant city,” Evans, 66, wrote in a brief letter that made no mention of the ethical lapses he’d committed. “It has been an honor and a privilege to serve.”

Mendelson, a longtime ally who had been urging Evans to surrender his seat, characterized the resignation as “a step in restoring the integrity of this institution and the trust of the public.”

Mayor Muriel E. Bowser (D) did not respond to requests for comment.

For months, Evans had assured friends and supporters — a broad network amassed over ­decades in the hurly-burly of D.C. politics — that the scandals he faced would pass and he would win another term in November.

Yet as evidence mounted that he had misused his office to help private consulting clients, ­Evans’s political footing grew more tenuous. Allies turned away, and the council stripped him of his prized chairmanship of the Committee on Finance and Revenue. He was forced to relinquish his leadership of the Metro board.

In early December, all 12 of Evans’s colleagues recommended his expulsion in a unanimous vote, setting him up to become the first lawmaker in D.C. history to face banishment.

Council member Mary M. Cheh (D-Ward 3), who oversaw the council’s internal investigation of Evans, described her colleague’s 29-year council career as “extraordinary” but also defined by “extraordinary ethical lapses.”

“He didn’t just slightly tiptoe over the line,” Cheh said. “He ran well past the line, and apparently for a long period of time. It is nevertheless a sad day for him, and a sad day for the council, that it had to come to this.”

The D.C. election board will schedule a special election to fill Evans’s seat for the remainder of the year. In recent weeks, as he mulled whether to resign, Evans also considered running for a new term, according to two people who spoke to him before the holidays. Six candidates are competing for the Ward 2 seat in the June 2 Democratic primary, which is tantamount to the general election in a deep-blue city. The filing deadline is March 4.

Over the course of his council tenure, Evans was a symbol of continuity at the John A. Wilson Building as six mayors came and went and as the District’s economic fortunes evolved from near-bust to boom, a turnaround for which he often claimed ­credit.

He faced scrutiny earlier in his career for his use of constituent and campaign funds, but he endured while the careers of fellow Democrats — including Mayor Marion Barry, council Chairman Kwame R. Brown, and council members Michael A. Brown, Harry Thomas Jr. and Jim Graham — were upended by scandal.

His political reign began in the late 1980s with his election to the lowest rung on the District’s political ladder: a seat on a Dupont Circle Advisory Neighborhood Commission.

In 1991, when then-Ward 2 council member John A. Wilson ascended to the chairmanship, Evans won Wilson’s seat, campaigning as an opponent of Dupont Circle development. It was Wilson whom Evans often credited for teaching him a fundamental fact of pragmatic politics: On a 13-member council, he needed only seven votes to get his way.

Evans presided over a ward that encompassed downtown and stretched from the affluence of Georgetown to what was then the poverty of Shaw. His constituents included business executives, socialites and lobbyists; gay people who were gentrifying ­Dupont Circle; and African Americans who had lived in the rowhouses and apartment buildings east of Logan Circle for generations.

A bon vivant, Evans navigated diverse constituencies with ease, whether at community meetings or charity galas, to which he often arrived in a tuxedo, ready to pose with luminaries for photos that ended up framed on his office wall.

Evans grew up in northeastern Pennsylvania and moved to Washington to work as a lawyer for the Securities and Exchange Commission. His constituents were well versed in the details of his personal life, including the birth of triplets in 1996 and the death of his first wife, Noel, who succumbed to cancer seven years later, at age 46.

As a widower, Evans managed the demands of raising his children while serving in his council post and working at a prestigious law firm.

He became an aggressive advocate for ambitious downtown development projects that helped redefine the city, including the Walter E. Washington Convention Center and what is now the Capital One Arena on Seventh Street NW. As finance committee chair, he was a dependable ally for the District’s tax-averse business community.

In the early 2000s, Evans helped then-Mayor Anthony Williams persuade Major League Baseball to move a team to Washington and pushed the council to build a ballpark on the banks of the Anacostia River, triggering an explosion of luxury development in a part of the city known for strip joints and warehouses.

For all his council accomplishments, Evans yearned for a bigger platform. Twice, he ran for mayor, hoping that his record of dealmaking would persuade a predominantly black electorate to embrace him, a blond white man whose blue suits and striped ties made him look like he had stepped from the pages of a Brooks Brothers catalogue.

It never happened, despite a gush of financial support from developers. In 1998, Evans won 10 percent of the vote. Sixteen years later, he ran again, often asking voters, “Is this city ready for a white mayor?”

“Not any white guy can win,” he would answer. “But I can win.”

He got 5 percent of the vote.

Ever the pragmatist, Evans quickly heaped praise on Bowser, whom he had dismissed as an inconsequential legislator during the primary campaign.

By then, he had survived several periods when his spending was questioned. In the early 2000s, he withdrew thousands of dollars from Jack PAC, his political action committee, for travel and entertainment expenses, ­including $6,772 for a friend to go to China with him. The Office of Campaign Finance recommended that he pay the money back.

In 2011, he was criticized for using more than $135,000 in constituent service funds — money intended to help residents with emergencies such as missed rent and utility payments — to attend sporting events. After defending the expenditures as “perfectly legal,” Evans over the next eight years spent more than $200,000 in constituent funds on Nationals, Wizards and Capitals tickets.

A more intense level of scrutiny began in 2018, after reporter Jeffrey Anderson of District Dig revealed the relationship between Evans and Don MacCord, the founder of Digi Outdoor Media, who sought the lawmaker’s assistance as he tried to install digital signs around the city.

The Washington Post later reported that MacCord gave Evans 200,000 shares of stock just before the council member proposed emergency legislation that would benefit the company. ­Evans said he returned the stock, along with $50,000 that MacCord paid him.

Last February, The Post revealed that a federal grand jury was investigating Evans and had sought documents from the city government about Digi.

Weeks later, The Post published business proposals that Evans had sent to law firms from council accounts in which he offered to use his influence and connections as an elected official and Metro board member to land clients. That prompted the council to reprimand Evans, the city ethics board to fine him $20,000 and the Washington Metropolitan Transit Authority to open an investigation.

That probe concluded that Evans violated the transit agency’s ethics code by failing to disclose that he was receiving $50,000 a year from Colonial Parking as he was “waging a campaign” against a competitor, Laz Parking, which held a Metro contract.

Evans and his allies tried to conceal the findings. After The Post reported them in June, Evans said he would step down from the board. A day later, federal agents searched his Georgetown home.

In July, the council voted to strip Evans of his committee chairmanship and launched its own investigation into his use of his public office and his consulting business. That same month, council member David Grosso (I-At Large) became the city’s first lawmaker to demand ­Evans’s resignation. Others urged patience.

Whatever hesi­ta­tion they felt had dissipated by early November, when the report from the council’s investigation was released. Findings included that Evans received $400,000 in consulting payments and failed to disclose his clients.

Under questioning from investigators, Evans struggled to explain the services he had provided for those fees. Investigators identified numerous instances when he had voted on legislation and contacted city agencies to assist his clients while they were paying him. Evans defended his conduct, saying he provided routine constituent services that he would offer to any business or person.

His colleagues rejected those explanations. Nine members urged Evans to resign. Mendelson said Evans had “obliterated the public trust.”

The preliminary expulsion vote was Dec. 3, with a final vote scheduled for Jan. 21.

At the council’s regularly scheduled breakfast Tuesday morning, Evans left his waffle mostly uneaten and was silent while his colleagues joked about plans for gambling regulations.

During a legislative meeting later in the morning, Evans could be seen speaking privately with Mendelson. He left the dais when the session ended and walked downstairs to his first-floor office, ignoring questions from reporters.

Evans left the building at 1:10 p.m. His spokesman, Joe Florio, said the council member had no additional statement planned.

Correction:An earlier version of this story incorrectly described where Jack Evans grew up. It was in northeastern Pennsylvania.