Assembly Speaker Carl Heastie is expected to endorse Zohran Mamdani for mayor Wednesday, becoming the latest political power player to line up behind the socialist front-runner as he has started to consolidate key Democratic support, according to a source familiar with the matter.

Heastie, one of New York's most influential Democrats, has since Mamdani's victory in June's mayoral primary kept him at arm's length, refraining from endorsing him.

A number of other top New York Dems, including Gov. Hochul, Senate Minority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries, similarly withheld support from Mamdani for months after his primary win, as some members of the party fretted the 33-year-old Queens Assembly member's progressive agenda could turn off certain voters.

But over the weekend, Hochul led the way in officially endorsing Mamdani, and on Wednesday morning, Heastie is expected to follow suit, the source told the Daily News, speaking on condition of anonymity.

Heastie, who is as Assembly speaker Mamdani's legislative leader in Albany, will offer the endorsement during a press conference in the Bronx, the source added.

A spokesman for Heastie, who represents portions of the northeast Bronx, didn't immediately return a request for comment Tuesday, and neither did a rep for Mamdani.

In Albany, Mamdani's democratic socialist wing has at times had a tense relationship with Heastie's more moderate faction.

Heastie's decision to give Mamdani his support comes as the Democratic mayoral nominee has cemented his position as front-runner, with a string of polls released this month showing him holding a commanding lead over his opponents.

The move from Heastie is likely to further ramp up pressure on both Schumer and Jeffries, New York's top Democrats in Congress, to also offer support for Mamdani. Heastie's nod could also stand to help Mamdani with Black voters, especially in the outer boroughs, a constituency he has since the primary tried to win over.

Mamdani is set to face off in the Nov. 4 election against Andrew Cuomo and Mayor Adams, both of whom are running on independent ballot lines, as well as Republican nominee Curtis Sliwa.

In polls of the race, Mamdani holds a big lead, with Cuomo, the runner-up, trailing him by about 20 points in most surveys.

The electoral math changes, however, in a one-on-one contest between Cuomo and Mamdani, with the ex-governor getting a better shot at victory in such a scenario.

To that end, there are efforts unfolding to get Adams out of the race, including an offer for him to join the Trump administration, though he continues to say he is staying in. Sliwa, for his part, has said he has no intention of dropping out.

N.Y. Assembly Speaker Carl Heastie, another major Dem holdout, set to endorse Mamdani for NYC mayor