Brian Michael Downey is an Irish drummer. He was a founding member of the rock band Thin Lizzy and the only other constant in the band aside from leader Phil Lynott until their disbandment in 1983. Downey also co-wrote several Thin Lizzy songs. Allmusic critic Eduardo Rivadavia has argued that Downey is "certainly one of the most underrated [rock drummers] of his generation".

Thin Lizzy are an Irish hard rock band formed in Dublin in 1969. Thin Lizzy initially consisted of bass guitarist, lead vocalist and principal songwriter Phil Lynott, drummer Brian Downey, guitarist Eric Bell and organist Eric Wrixon, although Wrixon left after a few months. Bell left at the end of 1973 and was briefly replaced by Gary Moore, who himself was replaced in mid-1974 by twin lead guitarists: Scott Gorham, who remained with the band until their break-up in 1983, and Brian Robertson, who remained with the band until 1978 when Moore re-joined. Moore left a second time and was replaced by Snowy White in 1980, who was himself replaced by John Sykes in 1982. The line-up was augmented by keyboardist Darren Wharton in 1980. The singles "Whiskey in the Jar" (1972), "The Boys Are Back in Town" (1976) and "Waiting for an Alibi" (1979) were international hits, and several Thin Lizzy albums reached the top ten in the UK. The band's music reflects a wide range of influences, including blues, soul music, psychedelic rock and traditional Irish folk music, but is generally classified as hard rock or sometimes heavy metal.