Baker’s environmental chief, Matthew Beaton, will leave the administration

Matthew Beaton. Keith Bedford/Globe Staff/File/2016/Globe Staff

Matthew Beaton, who has served as Governor Charlie Baker’s only environmental affairs secretary since he first took office, is decamping for the private sector after more than four years of helping shape the administration’s energy policy.

In his place, Baker tapped a former conservation consultant, Kathleen Theoharides, who has been his administration’s point person on climate change — a sign, advocates say, of the governor’s intent to underscore the issue.

Beaton, a former GOP state lawmaker, oversaw a sprawling state secretariat that includes parks, the Environmental Police, and the Department of Public Utilities — at a time when Baker has pursued massive clean-energy projects, tried to spur more solar energy production, and pushed addressing climate change to the top of his priorities.

But Beaton, 39, has also overseen agencies that, at times, became embroiled in embarrassing political scandals and faced calls from environmental activists to seek loftier goals.

He will join TRC Cos. as a senior vice president. The Lowell business does environmental consulting and engineering work and has been involved with the controversial Weymouth compressor station project, which earlier this year won key permits from the Baker administration.

Theoharides, who joined the administration in 2016, has helped lead Baker’s initiatives to combat climate change, including working directly with cities and towns through the Municipal Vulnerability Preparedness program.

The state has also been focused on reducing carbon emissions, though Theoharides, 37, declined to comment Monday on her position on carbon pricing.

Her appointment won early plaudits from advocates.

“I tell people if she wasn’t working [for the state], I could see her working at an advocacy group,” said Emily Norton, executive director of the Charles River Watershed Association.

“She really gets into the weeds and clearly cares deeply about doing things the right way,” she added. “For us in a science-based organization, that’s really terrific.”

Theoharides will take over for a secretary whom Baker has praised as the “ideal person” to run environmental affairs.

Beaton, an avid outdoorsman who had run a small green-building and energy-efficiency consulting company, helped lead the Baker administration’s efforts to bring the nation’s first large-scale offshore wind farm to the waters off Martha’s Vineyard, as well as its pursuit of a 145-mile power line through western Maine to import hydropower.

The administration has also sought to float more incentives for solar projects under Beaton, who said the state has spurred more development in the last four years than in “the entire history of solar development in Massachusetts.”

On climate change, Baker has proposed to increase the tax on Massachusetts real estate transfers by 50 percent, with a goal of funneling the more than $1 billion over 10 years toward local mitigation efforts.

“He mastered some pretty complicated issues, especially on the energy side,” Bruce Berman, a spokesman for the group Save the Harbor/Save the Bay, said of Beaton. “He knew from experience that the natural environment requires protection and investment, and I think he’s going to be remembered as a good secretary.”

Beaton’s tenure didn’t come without spurts of turmoil within the state agencies that he led, however.

In 2016, Matthew Sisk, a longtime Republican operative and state committeeman, was forced to resign after he used the blue lights on his state vehicle to get through rush-hour traffic in Boston.

Weeks earlier, he and the commissioner of the Department of Conservation & Recreation, Leo Roy, were suspended for a week without pay for using golf carts assigned to the Fourth of July events on the Esplanade to ferry a handful of GOP partygoers.

The next month, Michael Valanzola, a former GOP state Senate nominee, resigned, and his cousin Jared Valanzola lost his DCR job after officials determined that Jared had tried to force a co-worker to persuade her fiancé not to challenge a Republican state senator.

Beaton himself came under scrutiny in 2017, when he had to refund the state after he used taxpayer money to pay for a round-trip plane ticket during his Florida vacation earlier that year.

And in 2018, Colonel James McGinn, head of the Massachusetts Environmental Police and Baker’s former driver, was fired after a state review found he had fixed two tickets, installed unauthorized surveillance cameras, and hired a private investigator to follow an officer.

Beaton is the third member of Baker’s Cabinet to leave since Baker won reelection in November. Jay Ash, the economic development secretary, stepped down in December, just weeks after Daniel Bennett, the public safety secretary, decided to leave the administration.

In February, Lon Povich, who had been the only general counsel to serve under Baker, also left.