Born to a Scottish parents Charles Dempster and Eliza Jemima Weavers in 1903, Stewart “Stewie” Dempster lived the first three decades of his life in Wellington, nearby to the local cricket ground the Basin Reserve. Developing an early interest in the game Dempster played for the Wellington Boys' Institute team in his youth and was encouraged by his father to score hundreds, being rewarded with 5 shillings from him for each one he scored. In his most prolific season he scored nine centuries in ten innings with the remaining innings scoring 99 and gaining the attention of the local provincial selectors. In all first-class matches for New Zealand, Dempster scored 11 centuries, then another 18 for Leicestershire as he built a successful 14-year career in England before returning home and struggling to find his niche before entering coaching.

Dempster was an only child whose father, a sea captain, got into trouble with the law, and whose mother had a dalliance with a plumber that led to the divorce courts. Natural ability combined with relentless practice took him to the top of the batting tree - a giant step removed from some of the travails of his upbringing. Dempster also had a reputation as a "ladies man" who had a broken engagement and three marriages.

Dempster made his first first-class appearance for Wellington against Canterbury at the Basin Reserve over new year 1921/1922 scoring 10 and 1. Dempster first toured with New Zealand in 1927, when no Test matches were played, and headed the touring team's first-class batting averages. He was a surprise choice for the tour, being selected more for his performances in second-class cricket. In the 1929/30 MCC tour of New Zealand Dempster and Mills put on a New Zealand record first-innings stand of 276 for the first wicket, which remained the highest for New Zealand until 1972 .

Dempster scored that landmark century in New Zeand and 18 months later repeated the feat in his first offshore test at Lord's. His test career spanned just 10 matches and three years. In the 1931 New Zealand tour of England he averaged 59.26 and scored 120 in the Test at Lord's. The lad was just 24 when he travelled to England to cover the Kiwi cricket tour of 1931. It was quite a fruitful trip for him as well. He wrote a book on the visit, with the utilitarian name New Zealand Cricketers in England 1931, and it remains a valuable record in the cricketing archives. While in England he also met a girl called Flora Margaret McIver, or just Madge, and by November of that year they were married at Paddington, London. In 1932 he was listed as one of the Wisden Cricketers of the Year. Behind Bradman's stratospheric figure of 99.94, Dempster slots in with 65.72 ahead of a modern day great Steve Smith.

Dempster moved to England, appearing in one first-class match for Lindsay Parkinson's XI in 1933 and once for Scotland in 1934. He settled in England from 1935, being contracted by the Leicestershire millionaire Sir Julien Cahn to play for his private team. Dempster qualified for Leicestershire, captaining the team from 1936 to 1938, although playing irregularly in 1938 and 1939. In 1938/39, he toured New Zealand with Cahn's team. He was able to play county cricket as an amateur, and was therefore acceptable as a county captain, by being employed by Cahn, ostensibly as the manager of one of his furniture stores in Leicester. While there, he married Margaret Jowers from Leicester in 1938.

Dempster appeared for the County scratch sides during the war but left the staff when the war ended. He played three times for Warwickshire in 1946 before returning to New Zealand to become a coach. He was selected to play for New Zealand in a one-off Test in Christchurch against England in March 1947, but he withdrew due to an eye injury four days before the match.[6] The match ended in a draw. Dempster made his final appearance for Wellington against Auckland at Eden Park in January 1948 scoring 7 and 41.

Dempster has the distinction of having the second-highest Test batting average in history for completed careers of 10 or more innings, behind Sir Donald Bradman. After his retirement from playing, he was a prominent coach in Wellington for many years. His pupils included the Test players Bruce Edgar and Ian Smith. The boys he coached in his twilight years professed a love for the man who gently and quietly told them how to go about perfecting batsmanship.

His name adorns the northern entrance of the Basin Reserve, a lofted drive from where he grew up on Kent Terrace. Thousands of cricket fans and pedestrians stroll through the CS Dempster Gate, season after season, many without knowing the significance of the name to New Zealand Cricket. For the fleeting fan, Stewie Dempster may be the greatest New Zealand cricketer they've never heard of.