West Benhar, Lanarkshire born wing half Billy McKay began his football career with junior club Shotts Battlefield in 1924 before joining Scottish League East Stirlingshire a year later, spending two years there before joining Hamilton Academical in 1927. He was signed by First Division Bolton Wanderers in December 1929 and made his Football League debut the same month at Manchester United, quickly establishing himself as a regular first team performer. After Bolton were relegated in 1933, he was signed by Manchester United in March 1934 after 17 goals in 108 appearances for The Trotters.
He helped United to avoid relegation from the Second Division at the tail end of the 1933-34 season, and rise up the table to fifth position in 1934-35. He was then part of the successful promotion campaign of 1935-36, as United won the Second Division Championship. However they were relegated straight back down to the Second Division the following season, but McKay’s four goals in four games at the end of the 1937-38 season helped the club regain to secure runners up spot and therefore regain their First Division status. The Red Devils then finished 14th in the First Division in 1938-39.
McKay’s career was disrupted by the Second World War, putting at end to the Football League in the first half of the 1940s, though he did turn out for Manchester United in their wartime games. During the war he also made guest appearances for Stockport County and Port Vale. On resumption he joined Cheshire County League club Stalybridge Celtic in 1946, already aged 40, having scored 15 goals in 184 appearances for United.