Johnstone is most remembered as one of the Famous Five forward line (Smith, Johnstone, Reilly, Turnbull and Ormond) for Hibernian in the late 1940s and early 1950s. He joined Manchester City in 1955, becoming the first player to score in successive FA Cup Finals at Wembley, in 1955 and 1956. After a short return to Hibs he also played for Oldham Athletic.