Around campus, Unity College President Mitchell Thomashow, who recently announced that he will step down in July after five years at the school, has been a casual, even groovy presence. He wears socks around the office, and a pair of reading glasses with frames that in their colorful flamboyance suggest a box of melted crayons. He chats up students around campus and often hosts events and classes and events in his home, where again the shoes come off.

He’s a musician and avid player of games, both over-the-board and athletic — a signed, framed jersey in his office not a remnant of some glory years as a school athlete but a memento from a pick-up basketball league in Keene, N.H., but his casual demeanor belies what has been, particularly in the later years, an ambitious agenda.

Thomashow, 61, came to Unity in 2006 after more than 30 years at Antioch New England Graduate School at Keene, N.H., where he served as Chairman of the Environmental Studies Department and Associate Dean for Institutional Advancement.

During his tenure, Unity College has continued its transformation from a backwoods training facility for foresters and game wardens to a full-fledged, liberal arts college that has become nationally recognized for its focus on the environment.

When he was approached about the job, Thomashow recalled, a recruiter described Unity as a “diamond in the rough,” meaning there was a committed staff and the school had a strong outdoors orientation, but didn’t have a clear sense of its own future and promise.

Thomashow said the school now has that sense of direction. In a nutshell, he said, it’s about “sustainability,” a concept that Thomashow and Unity College have used to organize the sprawling disciplines of the liberal arts into five multidisciplinary “Centers for Academic Excellence” with names like the Center for Experiential and Environmental Education and the Center for Sustainability and Global Change. Within these centers the number of majors was trimmed from 25 to 15 — a change that Thomashow described as a “sharpening.”

Beyond the obvious environmental connotations of “sustainability,” many of Thomashow’s biggest accomplishments were aimed at sustaining Unity College. And he did this by pushing the school to be a player in the national and international environmental arena.

Unity House, a new president’s residence built in 2008 that produces more energy than it consumes, came about through a collaboration between Unity College, Thomashow’s college friend and innovative builder Tedd Benson, and the Massachusetts Institute of Technology, and has since become a showcase and a symbol of the school’s loftier ambitions.

Plans are currently underway to build a new residential “eco-cottage” that would serve as dormitories for about 10 students. The new facility would use passive solar technology.

Thomashow signed the American College & University Presidents Climate Commitment, and the school has experimented with buying carbon offsets. Recently, Unity College was one of 11 schools in the country to make the Princeton Review’s 2011 Green College Honor Roll.

Over the past two years, the school has made several high profile, ceremonial donations of solar panels that had been installed on the White House during the Carter Administration. The college came into possession of the panels in the 1990s, but until recently they had mostly remained in storage.

Earlier this year, the college gave one of the panels to Huang Ming, chairman of Himin Solar Energy Corp, China’s largest manufacturer of solar thermal equipment, for installation in a new solar energy museum in China. Huang, who has been described as the “Donald Trump of China,” traveled to Unity for the presentation.

Author and activist Bill McKibben made a highly publicized road trip with a second panel to the White House this summer in an effort to draw attention to the need for investments in renewable energy.

No college president has probably ever been universally loved, but several of Thomashow’s colleagues voiced praise for his work at the school.

“It’s been a sort of sunny season for the arts and humanities during this time,” said Unity College associate professor of art Ben Potter, who started at the school around the same time as Thomashow.

Potter credited Thomashow with putting substance behind Unity’s claim to being a liberal arts college.

“It’s put Unity on the map in the art community instead of [the school] just being a freaky barnacle outlier,” he said.

Tim Peabody, an associate professor in one of Unity College’s older programs, conservation law, in which about 120 students are enrolled, said the department has fared well under Thomashow.

“It’s always been a strong program at Unity. Under his leadership we still have a good program. As far as the overall mission of the college, I think he’s done well, especially in hard economic times,” he said. “And that’s all you can ask for.”

Thomashow said he and his wife Cindy plan to move to the West Coast to be closer to their adult children and to pursue several job opportunities there in the environmental field. Quitting one job before getting another is not the norm, he noted, but he wanted to give the college plenty of time to find a successor.

His announcement follows on the heels of the resignation of Unity’s Vice President for Academic Affairs, but the outgoing president expressed confidence in the senior staff of the school and board of trustees and said he expects a seamless transition.

“The college is doing extremely well financially and academically,” he said. “It’s a great time to hand it off to someone.”