File: Carol Schwartz, a former D.C. Council member, has announced that she will run for mayor as an independent. (Sarah L. Voisin/The Washington Post)

Carol Schwartz, a mold-breaking politician who served 16 years on the D.C. Council, said Monday that she will launch a late-breaking independent campaign for mayor — her fifth bid for the District’s highest office.

Although it has been more than five years since Schwartz appeared on a D.C. ballot, her surprise entry unsettled a mayoral race that had been shaping up as a duel between Democratic nominee Muriel E. Bowser and independent David A. Catania, both council members.

Shortly after Schwartz announced her intentions Monday afternoon, Catania’s campaign accused Bowser of playing a background role in Schwartz’s run in a bid to siphon votes that might otherwise go to Catania.

“I think it’s a clear signal of how worried and concerned the Bowser campaign is,” said campaign manager Ben Young, who noted that Schwartz supported Bowser in previous council runs.

Both Schwartz and Bowser denied any arrangement. “We knew she’s been interested in running for mayor,” Bowser said, a reference to Schwartz’s previous runs in 1986, 1994, 1998 and 2002.

Schwartz said Monday that she was compelled to join the mayoral race after becoming dissatisfied with both leading candidates. “I wanted somebody to vote for November 4 that I felt comfortable voting for,” she said. “I have known that since I have been around town for months that a lot of people feel the same way. So here is another choice.”

She declined to elaborate on her feelings toward either Bowser or Catania.

The fact that Schwartz, also a former Republican with years of name recognition, could cut most directly into Catania’s support raised the prospect that she may be running in part to deny the mayoralty to Catania, with whom she clashed frequently during her final years in office and whom she has blamed for her 2008 electoral loss.

Schwartz on Monday denied that Catania’s run had anything to do with her own decision: “This isn’t about anybody else running for office,” she said. “I want to be mayor. I’ve always wanted to be mayor.”

During her four terms on the council, Schwartz was an unusual presence in District politics — a Mississippi-born, Texas-bred white Republican in a mostly Democratic, African American milieu. But over three decades, starting from the city’s old elected school board to the council to her long-shot mayoral runs, she built one of the most memorable brands in city politics.

Schwartz, 70, has been out of politics since losing a 2008 reelection bid, falling to a Republican primary challenger backed by Catania, then failing to gain traction in a subsequent write-in bid. She has largely kept out of politics, saying she was happy to travel and spend time with family.

Schwartz said she decided less than two weeks ago to pursue the mayoralty and has little in the way of campaign infrastructure. She said she has no campaign chairman but has opened a bank account and has a treasurer. “My closest friends didn’t even know I was going to do this,” she said Monday.

Her announcement was e-mailed to reporters without forewarning Monday afternoon. It included a lengthy statement by Schwartz explaining why she is returning to politics and again pursuing the mayor’s office.

She cited the effects of the city’s explosive economic growth — “our glorious diversity is being threatened” — and the corrosion of public trust caused by recent political corruption.

“I want a leader who has the wisdom to recognize chicanery before the ‘you-know-what’ hits the fan and who has the courage to take it on and stop it before it hits,” Schwartz wrote. “I have not seen that leader in this general election. I may not be alone in this feeling, given the low voter turnout in the primary and the general lack of enthusiasm about this race.”

The closest Schwartz came to the mayoralty was in 1994, when she ran within 14 percentage points of Marion Barry, who was in the course of completing a comeback from his 1990 drug arrest. In her last run, in 2002, Schwartz finished 26 points and nearly 35,000 votes behind incumbent Anthony A. Williams.

But Schwartz was able to repeatedly win reelection to the council, taking advantage of not only her image as a socially liberal fiscal hawk but also a provision in the District’s charter that effectively reserves two at-large council seats for non-Democrats.

It’s unclear how much of her old voter base — such as the nearly 40,000 voters who cast write-in ballots in 2008 — will remain loyal today. Schwartz has been reticent to weigh in publicly on contemporary political debates.

On Monday, she was noncommittal when asked about several key issues now percolating through the John A. Wilson Building, including proposals to build a soccer stadium, redraw school boundaries and change firefighter work schedules.

Although Schwartz ran as a Republican in each of her council and mayoral races, she will run this time as an independent. She said she changed her voter registration from Republican back in December, a decision she declined to explain Monday: “If I talk about that, and I may, it’s not going to be a sound bite.”

Ron Phillips, chairman of the D.C. Republican Party, said he had asked Schwartz this year whether she would be willing to stand as the GOP nominee for mayor but Schwartz “respectfully declined.”

Phillips said the party plans to name its own nominee in the coming weeks, but he acknowledged Schwartz maintains support: “There are Republicans who have known her well through the years and will wish her well.”

Ballot petitions will be made available Friday for an eight-week circulation period. Independent hopefuls must collect 3,000 valid voter signature to secure a spot on the ballot.