Johnstone, Renfrewshire born wing half Jock Priestley began his football career with Scottish League club Johnstone in 1919 before joining First Division Chelsea in May 1920, making his Football League debut in a 0-0 draw away at Blackburn Rovers on the 2nd May 1921. He didn’t make another appearance for Chelsea until Boxing Day 1922, missing the 1921-22 season completely. Turning out for The Pensioners in a 4-0 win at Nottingham Forest, Priestley made a further 22 appearances during the season, scoring his first goal for the club in a 3-0 win against Bolton Wanderers in front of a crowd of 20,000 at Stamford Bridge.
The 1923-24 season saw Priestley make 42 appearances for Chelsea, scoring twice in victories against Middlesbrough and Manchester City, though he was unable to help the London club stave off relegation to the Second Division. In the following season, Priestley would again feature heavily for Chelsea as the side finished 5th in Division Two, missing out on promotion by 10 points. The 1925-26 campaign proved to be more fortuitous for Priestley as he quadrupled his goal tally from the previous year, despite making only six more appearances in all competitions for Chelsea, helping them to a 3rd-place finish in the League come the end of the season, narrowly missing out on promotion.
Priestley bettered his scoring record in 1926-27, having his most prolific year for The Blues with 7 goals in 44 appearances as Chelsea finished 4th. He netted twice from the penalty spot in a 2-1 win over Clapton Orient on New Year’s Day 1927 and scored twice again as Chelsea beat Bradford City a month later on 5th February. Though he only made 18 appearances in his last season (1927-28) at Stamford Bridge, Priestley still pitched in with four goals, netting his last double in a 5-2 home win against Bristol City. This would be Chelsea’s only victory after January 1928 with Priestley in the team as the club finished 3rd in Division Two, missing out narrowly on promotion once again.
In the 1928 close season he transferred to Grimsby Town after 19 goals in 204 appearances for Chelsea, and in his first season at Blundell Park, Grimsby won promotion to the First Division finishing as Second Division runners up with Priestley missing only 6 games. He continued as a mainstay of Grimsby’s first eleven for their next three seasons in the First Division before returning to Scotland joining St Johnstone in the summer of 1932. In 1933 he joined Cowdenbeath and finally finished his career with Highland League Keith, joining them in 1934.