Maryland Senate Majority Leader Robert A. Garagiola (D-Montgomery), once among the state’s brightest young political stars, said Wednesday he plans to resign his seat this fall and has no plans to seek elected office.

Garagiola, 40, who lost a Democratic primary for Congress last year that he was heavily favored to win, said his decision to step down was driven largely by his desire to spend more time with his three children, ages 15, 13 and 12.

“I’m an active and involved senator,” Garagiola said in an interview. “It’s very difficult to do the job I want to do and spend as much time as I want with my kids. . . . It is time for me to be a father first to them, and I realize as I watch them grow and become young adults that I won’t be able to get this time back.”

Garagiola, a member of the Senate since 2003, said he also had launched a law practice a year ago that was contributing to the challenges of juggling his responsibilities as a lawmaker and single father.

He did not rule out another run for elected office in the future. “One can never say never, but right now that’s not my plan,” Garagiola said.

A protege of Senate President Thomas V. Mike Miller Jr. (D-Calvert), Garagiola has been active on all of the major legislative battles of recent years, including a transportation funding package, same-sex marriage and a bill creating incentives to build an offshore wind farm.

An Army Reservist, Garagiola also founded and served as co-chairman of the Legislative Veterans Caucus in Annapolis, and he has championed measures to expand the use of solar energy.

Garagiola said he planned to leave the Senate when his term expires in January 2015 and more recently began thinking about stepping down sooner. His resignation will take effect Sept. 1.

The Montgomery County Democratic Central Committee will be tasked with recommending a replacement for Garagiola to Gov. Martin O’Malley (D). Several lawmakers and legislative aides suggested Del. Brian J. Feldman (D-Montgomery) would be the leading contender.

Feldman is one of three delegates who represent the same district as Garagiola.