A stalwart in defence during the late 1940s  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, he 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.

He only missed two games in his first season with the Grecians and followed this up with 37 and 41 appearances in the following seasons. He then developed knee ligament trouble following an injury in a game at Swindon Town in September 1950. Although he returned to the first team later in the season, the same injury flared up again in pre-season training in 1951. He was given a short term contract but was released in November 1951.

He had a testimonial match in October 1952 when Exeter City played a Cyril Johnstone XI.