The former Frederick County state senator announced his plans Saturday in a leter to the state party's central committee. Mooney said "it is time for me to pursue other ventures."
The anouncement comes after a grueling election year in which Maryland Republicans -- in addition to absorbing an expected shellacking in the presidential race -- lost one of their two remaining congressional seats and saw three party-supported referendum efforts go down to defeat.
Mooney is expected to remain in his unpaid, part-time post until March 1 to allow for an orderly transition. His successor will be chosen at the party's spring convention April 20. In the interim, party Vice Chairwoman Diana Waterman will serve as chair.
David Ferguson, the party's salaried executive director, said he will remain on the job after Mooney steps down.
Mooney, a staunch conservative known for his fire-breathing fund-raising letters, has been a fixture on the Maryland Republican scene since 1998. That year he came out of political obscurity to defeat veteran moderate GOP Sen. Jack Derr in the party primary. He served three terms before being narrowly beaten by Democrat Ronald N. Young in 2010.
He wasn't off the stage long, winning a four-year term as party chairman about a month later. After last year's election, in the weeks leading up to the December Republican state convention in Howard County, there were rumblings of discontent over Mooney's leadership, but nobody mounted a overt challenge to his continuance in that post.
In his letter, Mooney boasted that the party, despite its electoral reverses, improved its financial stability under his leadership. He said the state party raised $1.1 million last year -- far exceeding expectations.
A party source said that when Mooney was asked Saturday whether his resignation was a signal that he was considering a run against freshman Democratic Rep John Delaney in the Sixth District, the outgoing chairman said he was not closing any doors.
Such a race would be a long shot, however, because Delaney ousted longtime incumbent Republican Roscoe Bartlett by about 20 points in a district redrawn to favor Democrats.