Lonergan signed a five-year contract with George Washington on Friday to replace Karl Hobbs, who was fired last month.
Lonergan, 45, had a 126-68 record with the Catamounts since 2005, leading them to the NCAA tournament in 2010 as America East conference champions and to the NIT in 2007 and 2011. This year's team finished 23-9.
The move returns Lonergan to the nation's capital, where he won the NCAA Division III national title in 2001 with his alma mater, Catholic. Lonergan went 251-88 with the Cardinals from 1992 to 2004. During his last three seasons, he was coaching the men's team while his wife, Maggie, was coaching the women's team.
Lonergan was also born and raised in the nearby Maryland suburbs and went to high school in Washington, D.C. He left Catholic in 2004 and spent one season as an assistant under Gary Williams at Maryland before moving to Vermont, where he succeeded Tom Brennan.
"The opportunity to return to my roots in the Washington, D.C., area and build a program at an exceptional school like George Washington was too good to pass up," Lonergan said in a statement released by the school.
Lonergan will be formally introduced at a news conference on Monday.
The changes in the men's basketball program mark the first major moves under incoming athletic director Patrick Nero, who was hired last month. Nero was already familiar with Lonergan, having served as America East commissioner since 2005.
Lonergan takes over a program that struggled during the latter portion of Hobbs' 10 seasons at the school. The Colonials went 52-64 overall and 25-39 in the Atlantic 10 over the last four seasons.
However, Hobbs left the program on a bit of an upswing. This year's team finished 17-14 overall and tied for fourth in the A-10 with a 10-6 record in conference play. Lonergan, who met with the players for about 40 minutes Friday, inherits a team that is expected to return four starters and six of the top seven scorers.
"We've made it really clear that our expectation is to build on that," Nero said. "But we're not going to judge it on one year. We want to long-term build a program that can be competitive to the point of competing for the postseason, competing to be in the top third of the Atlantic 10, be in the discussion to be in the NCAA tournament and make it to the NCAA tournament. Those are our goals for this program."
Nero said he had four criteria in his search for a coach: academic success, reputation, ties to Washington and a winning track record. While Lonergan has all four, Nero cited one statistic that would be impossible for any coach to beat: He said Lonergan has a 100 percent graduation rate as a head coach.
"That's a streak we want to keep alive here," Nero said.