A stalwart in defence during the late 1940s and early 1950s Cyril Johnstone played for Exeter City between 1947 and 1951 having joined the club from Hamilton Academical. His career at St James' Park ended through injury.

Playing for his home town team Hamilton Academical, Cyril moved south to Exeter City in July 1947 and immediately won a regular first team place after making his debut at St James’ Park against Reading.

Appearing in both full-back positions, Cyril only missed two games in his first season with the Grecians and followed-up with 37 and 41 league appearances in the next two seasons before developing knee ligament trouble after an injury at Swindon Town in the eighth game of the new season in September 1950. Although he returned to the first team later in the campaign, the same injury flared up again in pre-season training in 1951, and given a short-term contract, Cyril was released in November 1951.

Cyril's final league match had been against Nottingham Forest in April 1951 and he was awarded a testimonial match in October 1952 when Exeter City played a Cyril Johnstone XI.