In October 1959 he earned his first international cap when he scored in a 4–0 win over Northern Ireland. In September 1962 he signed for Sunderland for £25,000. Mulhall played more 250 appearances for Sunderland, where he still holds the record for the most consecutive appearances for the club - 125 - and scored 55 goals. He won another two caps, also against Northern Ireland, before moving to South Africa to play for Cape Town City. He stayed for three seasons before playing one final game for Greenock Morton.
Mulhall moved into coaching upon his playing retirement first becoming trainer-coach at Halifax Town where he was promoted to first team manager in 1972. He was in charge until September 1974. A month later he moved to Bolton Wanderers where he spent four years as coach and assistant manager.