The Massachusetts Senate’s longest serving member, Marc Pacheco, known for his work on climate change and the service privatization law named after him, said Tuesday he does not plan to seek re-election.

The decision continues a trend this legislative session of veteran lawmakers deciding against another term for retirement or to run for other elected positions, moves that will spark races to replace longtime incumbents who have dominated their districts for years.

Pacheco, a stalwart of the Senate who was first elected in 1988, said his departure does not close the door on his work in public service.

The 16-term Democrat from Taunton announced the news in a post on social media in which he also revisited his work around organized labor, local efforts to keep a hospital open, and a push for a new judicial complex in Taunton.

He was the founding chair of the Senate’s Global Warming and Climate Change Committee, where he led an effort to pass the 2008 Global Warming Solutions Act, which ensured a cap on carbon emissions.

“While I am proud of all the work we have accomplished, much still needs to be done,” he said. “I look forward to working with my colleagues and everyone who is interested in making Massachusetts a better place to live; and while I am unsure what the future will bring, the door is always open for new and exciting opportunities.”

Pacheco had $164,108 in his campaign account as of Feb. 5 after raising just over $1,700 in January and more than $24,000 in December, according to state records. He chairs the Senate Post Audit and Oversight Committee and the Emergency Preparedness and Management Committee, and is the vice chair of the Telecommunications, Utilities, and Energy Committee.

Pacheco’s planned exit from Beacon Hill is the second to be announced in the Senate this session. Sen. Susan Moran, a Falmouth Democrat, said last year that she is not running for re-election, which prompted a race to fill the seat between two House colleagues.

But the turnover of seasoned lawmakers is more pronounced in the House, where at least six representatives who either hold a leadership position or a ranking committee spot have said they are not planning a return to the State House.

That includes Reps. Sarah Peake of Provincetown and Ruth Balser of Newton, who serve as the second assistant majority leader and third division chair, respectively, two leadership roles that come with boosted pay and responsibilities.

Peake, a nine-term Democrat, made her plans clear last month, saying in a statement that it had been the “honor of my lifetime to serve the wonderful people of the fourth Barnstable district for these past 18 years.”

“It has been my honor to be there for my constituents when they needed help untangling the red tape of state government, and to help craft legislation making sure our environment, economy, and way of life can thrive here on the outer and lower Cape,” she said.

The House will also lose at least three committee chairs, including Rep. Paul Schmid, who co-leads the Agriculture Committee; Rep. Denise Garlick, who co-leads the Education Committee; and Rep. Gerry Cassidy, a five-term Democrat from Brockton who co-chairs the Veterans and Federal Affairs Committee.

Schmid, a seven-term Democrat from Westport who was one of the inaugural co-chairs of the Agriculture Committee, pointed to his work serving farmers and bringing “local, healthy food into our schools and urban areas.”

“I want to thank everyone who has had confidence in me,” he said. “Many say the Southcoast delegation is the best and I have been honored to work with each member.”

Garlick, a six-term Democrat from Needham, said she plans to “work hard” during the rest of the legislative session, which ends Dec. 31, and is “humbled” to have represented people of all ages and abilities in Needham, Dover, and Medfield.

“I appreciate each of you for your courage, candor and continued conversations in the belief that good government can and does make a difference. I am grateful for your support and many friendships,” she said in a statement.

Rep. Smitty Pignatelli, an 11-term Democrat from Lenox, also said last week he is not running for re-election. He is the vice-chair of both the House Rules Committee and Joint Rules Committee.

“It’s been an honor of a lifetime to serve with some amazing people making our Commonwealth special. It’s NOT a retirement but the close of one chapter and the opening of a new one. More to come,” he said in a statement.