Newcastle born outside right Len Duns started his football career with junior clubs West End Albion in 1931 and Newcastle West End in 1932. Clearly an exceptionally fast athlete, he was a north east track champion as a youth before he joined First Division Sunderland in October 1933. He made his Football League debut for The Wearsiders at Portsmouth in November 1935, scoring a brace in his second game a few days later against Preston, and he won a League Championship medal that year scoring 5 goals in 18 appearances during his debut season.
He won the FA Cup in his second season scoring 5 goals in the earlier ties as Sunderland won the 1937 Final 3-1 against Preston North End at Wembley, a season in which he scored 21 goals albeit not surprisingly he finished behind Bob Gurney and Raich Carter in the scoring charts. He continued playing for Sunderland both sides of the Second World War, which significantly interrupted his career, albeit from 1949 with less regularity, and by the time he played his last game in March 1952 he had scored 55 goals in 248 appearances. He joined non league Ashington in the summer of 1952 where he finished his career.