Kathleen Theoharides, the Baker administration's point-person on climate change, will replace departing Energy and Environmental Affairs Secretary Matt Beaton (right). State House News Service Photo | Sam Doran

Energy and Environmental Affairs Secretary Matthew Beaton said Monday he would step down this week after more than four years leading the Baker administration’s clean energy and land conservation efforts to join a national environmental consultancy based in Lowell, creating an opening that the governor will fill with his administration’s top climate change official.

Beaton, who joined the administration in 2015 from the legislature, led the administration’s ongoing efforts to have the country’s largest offshore wind farm built off the coast of Martha’s Vineyard and to support a new transmission line through Maine to import hydroelectric power from Canada.

He plans to leave Beacon Hill at the end of the week to take a position as senior vice president of renewable energy and emerging technology at TRC Cos., which has done work on the controversial Weymouth compressor station project and has a national client list that includes many utilities and fossil fuel companies.

The company, which is headquartered in Lowell’s Wannalancit Mills, has offices around the country, and describes itself as an “engineering, environmental consulting and construction management firm” that provides services to clients in the “power, environmental, infrastructure and oil and gas markets.”

To replace Beaton, the governor turned to Kathleen Theoharides, the state’s first undersecretary for climate change who is affectionately known to staff as “Climate Katie.”

Theoharides was recruited to the administration by Beaton in 2016, and “spearheaded” the administration’s program to help municipalities identify threats and plan for climate change. Baker credited her with “nudging, cajoling and convincing people that this is something that we ought to be taking seriously, we ought to be working on, and we ought to be finding the solution together to deal with it.”

Beaton, a Shrewsbury Republican and former state representative, was one of Gov. Baker’s earliest cabinet selections after he won the 2014 election for governor, and he becomes the third member of the cabinet to step down since Baker won a second term in November. Theoharides will be sworn in on Friday.

As a member of the legislature, Beaton was one of the go-to Republicans in the House on energy issues, including the development of the solar industry in Massachusetts. Baker at the time said he wanted Beaton to “spearhead the administration’s push for energy efficiency, conservation and enhanced outdoor recreation,” and on Monday he said his secretary had delivered.

“Matt was always one of those people who knew what I was calling about and what I wanted to talk about and he usually had one, two or three of his kids hanging off him and sometimes he was out kayaking or fishing or sitting in a tree stand,” Baker said.

Beaton also weathered several scandals during his tenure atop the Executive Office of Energy and Environmental Affairs, including several at the Department of Conservation and Recreation, where one official was forced to resign for using blue lights on his state-vehicle to get through traffic, and another who was suspended for using golf carts meant for the Esplanade to ferry Republican party-goers to the Fourth of July fireworks.

A environmental engineer by trade, Beaton ran his own energy efficiency consultancy before joining the administration, and built for himself the state’s first “passive” home, which needs no furnace and almost no heating or cooling systems.

Beaton’s departure comes with three-plus years left in Baker’s second term, and amid efforts within state government to accelerate the pace of carbon emission reductions, including initiatives to extract reductions from the transportation and building sectors.

“I’m going to roll up my sleeves and take a good look at everything we’re doing and all of the great work Secretary Beaton has done before I comment on any specific issues, but I think we have identified that transportation is certainly part of our work to get to a clean energy future,” Theoharides said.