Brolly made his Derry Senior debut against Cavan in the 1990 National League. In 1993 he was part of the Derry side that won the Ulster Championship and the county's first All-Ireland Senior Football Championship. His All Stars Award recognition surprisingly came in the relatively barren years of 1996 and 1997. He was top scorer in the 1997 Ulster Championship with 3–15 (24 points). Brolly added a second Ulster Senior Football Championship in 1998, in the final of which he scored the clinching goal in the last minute. Derry won the National Football League four times in a nine-year period from 1992 to 2000 (1992, 1995, 1996, 2000), with Brolly being part of all four. Brolly and Derry finished runners-up to Offaly in the 1998 National League decider.