Sylvester Barrett was born in Darragh, near Ennis, County Clare, in 1926.[2] His father Frank, who was a founder-member of Fianna Fáil, and his mother Delia Costello, both died in 1931. As a result, he was raised by an uncle and aunt.[2] His brother Fergus (Patrick) Barrett OFM, became a Franciscan priest, and founding rector of St John Vianney Seminary, Pretoria, South Africa. Barrett was educated at Ballyea National School and St Flannan's College in Ennis. He studied engineering at University College Galway, though did not complete his studies.[2] He was a cadet in the Irish Army and later worked as a rate collector and an auctioneer.[3]
In October 1982, when Charlie McCreevy put down a motion of no confidence in Haughey's leadership, Barrett was the only Minister of State among the so-called Gang of 22 who supported it; Haughey survived, and did not dismiss Barrett from office.[2]