The man accused of sparking a summertime mass shooting in Brooklyn that left one person dead and 11 others shot has been arrested for murder, police said Wednesday.

Kyle Williams, 20, was busted for the murder of 38-year-old Jason Pagan at the Old Timer’s Day block party in Mendoza Park in Brownsville on July 27, cops said.

He was also hit with criminal possession of a weapon, reckless endangerment and attempted murder charges, authorities said.

Williams fired at Pagan, a reputed Bloods member, after the pair got into an argument about an old beef at the event, police sources said. Pagan was hit in the head and later died, cops said.

Investigators believe a friend of Pagan — who is still at large — returned fire, sparking a shootout that injured 11 other people at the party.

One survivor of the shooting escaped with just a graze wound, because her bra strap stopped the slug, her relatives told The Post after the shooting.

Williams was being held at the 73rd precinct Wednesday night, cops said.