Doug St John attended Otago Boys' High School, where he won the award for most improved player in the cricket team in his second-last year, 1944. He went on to study commerce at the University of New Zealand. St. John made his debut on 1 January 1947, against Auckland. Batting at six for Otago, he scored 28 and 31, and took two catches but could not stave off a one wicket defeat. He went on to play two more matches that season; scoring eight and eight not out against Wellington on 31 January, six and 25 in a drawn game against the Marylebone Cricket Club on 25 March. He ended his first season with 106 runs from three matches at 21.20, with a best of 31. At the start of the next season, St. John scored 85 and five not out against Wellington on Christmas Day. He would go on to play five matches in total, scoring a career-best 278 runs at 34.75, with two half centuries. He was selected to play for South Island in the match against North Island at the end of the season, scoring 47 and 63. His batting and sharp fielding in the match were noted, and he was named alongside John Reid as a promising player who might be selected to tour England in 1949. He struggled with the bat during the next few seasons, scoring only 102 runs during 1948/49 at 20.40 with a best of 53, and 117 during 1950/51 at 16.71, followed by 92 runs at 13.13 and 146 runs at 18.25 during his first two seasons at Wellington. He improved, however, during the 1954/55 season, where he scored 213 runs at 21.30, including a career-best 88. This came against Central Districts on 7 January 1955. Opening the batting - as he often did after moving to Wellington - St. John's 88 was bettered only by Test cricketer John Reid's 106 as Wellington pursued Central District's first innings score of 183 all out. St. John made 15 more runs in the second innings as Wellington reached victory by four wickets. The following season was to be his last, however, and saw St. John play five matches, scoring 182 runs at 20.22 with a best of 52 - his only half century of the season, which came in his final match. He bowed out on 10 February 1956, against a touring West Indies side that included Garfield Sobers. St. John scored his 52 in the first innings before being caught by Sobers, and made 19 as Wellington were forced to follow on and fell to an innings defeat.
