State Representative Garrett Bradley, a Hingham Democrat and senior member of House leadership, will step down after the legislative season ends next month, he told the Globe on Monday.

Bradley said he would take a more senior role at his Boston law firm and that he informed House Speaker Robert DeLeo of his decision last week. The second assistant majority leader said he planned to formally notify colleagues on Monday.

Bradley’s resignation will take effect on Aug. 1, after lawmakers have wrapped up an increasingly complicated and contentious season of formal sessions.

Joining the House in 2001, Bradley, a partner at the Thornton Law Firm, has represented a South Shore district that also includes Hull, Cohasset, and part of Scituate.

Bradley said he wanted to spend more time with his oldest child, who is applying to college. His wife, Heather, is first justice at Hingham District Court.

The move plucks a key ally from DeLeo’s leadership team. Bradley has sometimes served the speaker as an enforcer with other lawmakers on contentious matters.

Bradley’s first bid for the seat, in 1998, was unsuccessful. Then a young attorney, he took on longtime House Republican Mary Jeanette Murray, who had served in the Marine Corps during World War II.

Jim O’Sullivan can be reached at jim.osullivan@globe.com. Follow him on Twitter at @JOSreports.