D.C. Councilman David Catania addresses Kaya Henderson, D.C. Public Schools Chancellor, at the Wilson Building during a review of school closures Nov. 15, 2012, in Washington, D.C. (Katherine Frey/The Washington Post)

D.C. Council member David A. Catania is planning to file papers Wednesday to create an exploratory committee for a mayoral run.

His intentions were confirmed by former council member Sharon Ambrose, who said she will lead the committee. Catania (I-At Large) declined to comment Tuesday night.

“I think that there are very few council members . . . who work as smart and as hard as David has,” said Ambrose, a Democrat who represented Ward 6 from 1997 to 2007.

The move adds a new dimension to the city’s already crowded mayoral race, raising the possibility that the contest could remain competitive well past the April 1 primary.

Catania is perhaps the council’s fiercest critic of Mayor Vincent C. Gray (D), who announced Monday his intention to seek reelection.

As an independent, Catania would run on the November ­general-election ballot against the primary winners. He would not have to make a final decision about whether to run until June, when nominating petitions become available — allowing him to see first who emerges from the Democratic primary.

No non-Democrat has been elected mayor since Congress granted the District home rule in 1973. The closest any has come was in 1994, when Republican Carol Schwartz lost to scandal-scarred Marion Barry, 56 percent to 42 percent.

Ambrose said Catania can overcome the city’s overwhelmingly Democratic electorate. “I really think that the District of Columbia is entering into a new kind of political paradigm,” she said. “I think that we are really a ­post-partisan city.”

Catania, 45, was first elected to the council in a 1997 special election, becoming its first openly gay member. Initially elected as a Republican, he became an independent in 2004, breaking with the GOP over President George W. Bush’s support for a constitutional ban on same-sex marriage.

A lawyer, Catania is known for a prosecutorial bent and having the council’s sharpest tongue, sparring with colleagues on the dais and using oversight hearings to hold executive-branch officials to account — and in some cases, his critics say, to micromanage and browbeat them.

As chairman of the council’s Health Committee from 2005 through 2012, Catania promoted the expansion of basic health-care services and insurance coverage, and he crusaded to maintain the only city hospital east of the Anacostia River, now known as United Medical Center.

A $79 million city bailout orchestrated in 2008 with then-Mayor Adrian M. Fenty stabilized the long-troubled hospital but backfired when the hospital’s new private owner defaulted on its financial obligations. The hospital now is in the city’s hands and is in the midst of a new turnaround effort. Meanwhile, the District, in part because of Catania’s efforts to expand the city’s public ­health-insurance programs, now enjoys one of the highest rates of insurance coverage in the country.

In January, Catania took the helm of the council’s Education Committee, and he has pursued issues including test security, social promotion and school funding. In June, he introduced seven wide-ranging bills that he said would accelerate the city’s closely watched school improvement efforts and lift student achievement.

The council gave final approval to two of those bills Tuesday and gave tentative but unanimous approval to a third measure that would send more money to schools to help at-risk students.

Catania, almost halfway to making good on his promise to visit the city’s more than 200 traditional and charter schools, has accused Gray of sluggish and uninspired leadership of the city’s public schools. Gray has countered that the schools are on the right course, steadily improving and attracting more families every year.

District political observers have long considered Catania a potential mayoral candidate. He has declined to confirm his interest in the job in recent months even as he has traveled the city, talking several nights a week with likely voters in school PTAs and civic associations.

In those public appearances, Catania focuses on his priorities for public education, including his recent proposal to establish a new financial-aid program that would give high school graduates up to $20,000 a year for college.

“The more he’s gotten into the whole education picture, the more he’s become convinced education is the key,” Ambrose said. “I could not agree with him more.”