In an abrupt departure that could reorder Massachusetts politics, House budget chairman Brian S. Dempsey — widely expected to be the chamber’s next leader — is resigning and joining one of the state’s top lobbying firms in September.
His announcement turns what was anticipated to be an orderly transfer of power to succeed Speaker Robert A. DeLeo, when he eventually steps down, into a potential free-for-all over one of the state’s three most powerful political posts.
Dempsey’s sudden exit upends a hierarchy that has existed for years, injecting volatility into internal House dynamics. While rumors of Dempsey’s plan circulated Wednesday evening, members of DeLeo’s senior leadership team were unaware of them as late as Thursday morning.
“That’s a major, unanticipated shake-up,” said Representative Jay R. Kaufman, a Lexington Democrat, when told of the news by a reporter.
Dempsey is just the latest lawmaker to pass through Beacon Hill’s revolving door, where a well-worn path often leads to a more lucrative government affairs post seeking to influence the decisions of former colleagues.
Dempsey, who will serve as senior vice president and chief operating officer of ML Strategies, joins a steady exodus of top DeLeo deputies. The speaker will now have to select his third budget chief since winning the House’s top post in 2009.
Two years into his speakership, DeLeo demoted both his budget chairman and majority leader — both roles viewed as stepping stones to the speaker’s chair.
In 2015, at DeLeo’s behest, the House overwhelmingly voted to get rid of term limits for the speaker, extending his reign indefinitely and obscuring when another representative would ascend.
In a telephone interview, Dempsey denied that DeLeo’s apparent intention to hang onto the gavel for a few more years factored into his decision to leave.
“The speaker staying has never been a factor for me. He’s always had my full support for as long as he wants to stay,” the chairman of the House Committee on Ways and Means said.
Speaking to reporters at the State House, DeLeo on Thursday praised Dempsey, called him a “close and dear friend,” and said he would be missed.
DeLeo did not directly answer a question about how much longer he plans to stay in his leadership role. But he said he is running for reelection next year.
Asked who would take the reins of the powerful budget-writing committee when Dempsey leaves, DeLeo said, “That process will start now in earnest.”
Already, the halls of the State House were buzzing with the names of potential Dempsey successors, including the committee’s current vice chair, Stephen Kulik of Worthington, and Representatives Alice Peisch of Wellesley, Thomas A. Golden Jr. of Lowell, Sarah K. Peake of Provincetown, Joseph F. Wagner of Chicopee, Michael J. Moran of Brighton, and Peter V. Kocot of Northampton.
DeLeo’s choice could shape the trajectory of the Legislature for years to come. He and Dempsey are often seen as ideologically aligned on the more conservative end of the Massachusetts Democratic spectrum. A more progressive choice would bring the House closer philosophically to the left-leaning Senate.
Dempsey’s announcement comes as lawmakers are gearing up to host their state legislative counterparts from across the country for a national conference next month.
Such occasions often permit ambitious members to wine and dine colleagues, and the vacuum created by Dempsey’s exit will only heighten the stakes for this year’s interactions.
Already Thursday, lawmakers were jockeying to exert influence over who would succeed Dempsey in the House’s insular power structure.
“I believe now is the time for the Massachusetts Black and Latino Legislative Caucus, the Progressive Caucus, the Women’s Caucus to be strong and united in our selection of the next speaker of the House,” said Representative Russell E. Holmes, a Mattapan Democrat. “We should not do this individually; we should do this together so our voices are heard.”
The legislative advocacy community — lobbyists — had spent years cultivating relationships with Dempsey and his staff, working to get cash for their favored causes in the $40 billion state budget.
They had long labored with the expectation that he would ascend to the role of speaker. Now, they will compete against him for clients.
As the news broke Thursday, one lobbyist sent Dempsey an e-mail with the letter “n,” followed by several o’s — nooooooo.
While DeLeo on Thursday praised Dempsey, several people familiar with the inner workings of the House said there had been conflict about scheduling during the House’s budget deliberations in April. In recent years, floor deliberations that once took a full workweek and featured extensive debate have been compressed.
This year, the House wrapped up “budget week” in two days. DeLeo, according to those familiar, had hoped to prolong the process.
ML Strategies chief executive Stephen P. Tocco said he had signaled to Dempsey some months ago that he would be interested in talking with him if and when the legislator decided to leave the House.
“But I told him I can’t talk to you about anything until you file with the ethics commission,’’ Tocco said, referring to the state ethics law that requires such public disclosures and which Dempsey submitted Tuesday.
On Thursday, Dempsey said, “I told the speaker on Monday that I was approached and that I’d thought about it and that I was interested enough to go forward, file a disclosure, and have a conversation.”Frank Phillips of the Globe staff contributed to this report. Joshua Miller can be reached at email@example.com. Jim O’Sullivan can be reached at firstname.lastname@example.org.