Quincy representative Ronald Mariano in line to become Massachusetts Speaker of the House by mid-week

House Speaker Robert DeLeo will resign as of 6 p.m. Tuesday

House Speaker Robert DeLeo (left) and Majority Leader Ron Mariano.Globe Staff file

Lawmakers are poised to elect Ronald Mariano of Quincy as the next speaker of the Massachusetts House of Representatives Wednesday, just two days after the longest-serving speaker in state history announced his resignation.

The Democratic members of the House, who represent the overwhelming majority, will hold a remote caucus on Wednesday at which Mariano will be nominated to succeed Speaker Robert A. DeLeo. Boston state representative Russell Holmes, who launched a last-minute campaign for speaker, withdrew his name from consideration on Monday.

“I simply didn’t have the votes,” said Holmes. ”I made many, many calls and spoke to much of the body. I enjoyed the process — every minute of it.”

Mariano, 74, the current majority leader, has been collecting votes for speaker for years and is expected to capture more than 110 votes out of a possible 126 Democrats, including those of members considered much more progressive than he is.

DeLeo, the longest-serving speaker in state history, announced on Monday that he would resign Tuesday at 6 p.m. He is expected to take a job at Northeastern University. He did not say what his job will be or when he will start. A Northeastern spokesman said simply that, “pending ongoing conversations, we are looking forward to welcoming Speaker DeLeo back to his alma mater.”

DeLeo, 70, announced his departure in a letter that was read to representatives in the House chamber on Monday.

“It has been an honor and a privilege serving as a member of this institution for almost 30 years,” the letter said. “The faith and trust my colleagues placed in me by electing me as their speaker for a record six consecutive terms fills me with a profound sense of gratitude and appreciation. My pride with what we have collectively accomplished over the last 12 years will never be diminished.”

“This House has consistently led the way — and provided solutions to some of the most complex and challenging public policy problems of our time,” the letter said.

DeLeo also said he knew that the “House is well positioned for continued success.”

Applause erupted when the letter was read.

Other legislators and politicians, including Mariano, Governor Charlie Baker, and Boston Mayor Martin Walsh, responded to DeLeo’s announcement with well-wishes and praise.

“Speaker DeLeo will leave office with an impressive list of accomplishments. I look forward to celebrating his achievements tomorrow as he bids farewell to the House of Representatives,” said Mariano in an e-mailed statement.

In the statement, Mariano confirmed that he is seeking the speakership and said he’s “confident that my colleagues will elect me to lead the House through the remaining days of session. We have a lot of work to do overriding budget vetoes and completing conference committee negotiations. I am focused on seeing that work continue uninterrupted.”

Baker praised DeLeo’s “work ethic and sense of balance.”

“He put in the time, and on many issues — gun control, domestic violence, child welfare, wage parity, transportation, education, criminal justice and police reform,” said Baker in a statement. “He worked hard to find common ground among competing voices. That focus on deliberation and discussion made the end result better, and has created a positive, lasting legacy across state government.”

Walsh called DeLeo “a dear friend who I’ve had the unique privilege to work alongside during my years in the legislature and as Mayor. Having seen his leadership firsthand, I can say without hesitation that he has improved the lives of countless people throughout the Commonwealth,” Walsh said in a statement.

Senate President Karen E. Spilka, in a statement, offered “my sincerest congratulations to my partner and friend, House Speaker Bob DeLeo, as he embarks on the next chapter of his long and accomplished career.”

Aaron Michlewitz, House Ways and Means chairman, praised DeLeo’s leadership, saying he has shepherded the passage of measures that have had a “profound impact on all our constituents’ lives.”

Michlewitz added, “He’s treated everyone in this building with the utmost respect, regardless of the position you hold. People who know him and have worked with him know how much he empowers members to make meaningful impact.”

In electing Mariano, lawmakers will be turning to a veteran Quincy politician who has long sat at DeLeo’s side. A moderate Democrat, the 74-year-old has headed the Legislature’s financial services committees, served in leadership since 2009, and has regularly helped lead the House’s negotiations with the Senate on high-profile legislation, including on criminal justice and gun control.

Tackey Chan, a state representative from Quincy, said he is “very proud” that the next speaker will come from his hometown.

“It would be the first time in 82 years that we would have a Speaker from south of Boston and the first time since 1779 that the Speaker would be from Quincy,” he said. “This is historic.”

Two outgoing Democrats urged progressive lawmakers in a CommonWealth Magazine op-ed on Dec. 20 to push back on Mariano’s expected ascension, saying it will be in the “service of a center-right agenda.” Jonathan Hecht and Denise Provost also cited the fact that Mariano was one of only a few Democrats last year to vote against advancing a constitutional amendment, known as the “millionaires tax,” that would subject those making more than $1 million to an additional 4 percent surtax.

But Mariano’s supporters say he has gotten the backing of more than 110 lawmakers, well above the 81 he needs to become speaker. That includes the cochairs of the House Progressive Caucus, both of whom said they, too, would vote for him to succeed DeLeo.

The leadership change comes as lawmakers are already scrambling to complete their unfinished work. After giving themselves until Jan. 5 to wrap up formal business, a variety of complex bills — including an economic development package, a multibillion-dollar transportation bond bill, and climate change legislation — remain tied up in closed-door negotiations, with little clarity on when, or if, they will emerge.

How Mariano would operate as speaker is also unclear, given the immense power the role holds.

In leading the House for nearly 12 years, DeLeo held a tight grip on which bills flow to the floor, who receives powerful committee appointments and other assignments, and ultimately, what becomes law.

The Winthrop Democrat has been famous for rewarding loyalty and punishing members who disagreed with him, publicly or in private, and some former representatives have described him and his deputies wielding a top-down style of management.

DeLeo set the mark in February for longest-serving Massachusetts speaker, a record previously held by a 19th-century Federalist. That longevity made DeLeo an oddity in a chamber often defined by its turnover and, in political circles, a constant source of speculation about his next move.

DeLeo took the gavel in 2009 vowing to steady a House upended by the resignation of Salvatore DiMasi, who would become the third straight speaker convicted of a federal crime.

That vow included installing term limits, which were later undone, and pledging to “restore public confidence in the government.” DeLeo’s name came up repeatedly in the state probation department corruption trial in 2014, though he was never charged in the matter and lashed out at federal prosecutors who labeled him an unindicted co-conspirator.

An appellate court in 2016 overturned the convictions of three probation officials in the case, ruling that their actions, while distasteful, did not violate state law.