David McIntosh Turnbull was born in Winnipeg, Canada in 1906. He was the son of Janet (McIntosh) and William Turnbull, a graduate of the school of Medicine at the University of Manitoba in 1904.

David attended the University of Manitoba from 1924 to 1928 where he obtained a Bachelor of Arts in Mathematics. In his final year he was the senior stick for the Faculty of Arts and was awarded the Manitoba Rhodes Scholarship to attend Oxford. At Oxford he obtained a Bachelor and Masters of Arts in Philosophy, Politics and Economics, graduating in 1931. During his time at Oxford University he was accepted as a member of the University Ice Hockey Team in 1928 and played for the team at the Spengler Cup in 1928 and 1929.

Turnbull returned to Winnipeg, but in 1931 relocated to Toronto where prospects were believed to be better. That year he joined Manufacturers Life, but two years later he was hired by the firm Woods, Gordon and Co. as a "time-study man". Employed within the firm’s work measurement services department, Turnbull was primarily concerned with time and motion, marketing, supervisory training and organizational studies. In 1952, he opened the firm’s Montreal office where he remained in charge for the next twelve years. Upon his mandatory retirement as a partner in 1964, he moved to the Toronto office to assist the University of Toronto’s Faculty of Medicine in its expansion project. He fully retired in 1972 and pursued his own interests until his death on December 26th, 1995.