He worked for the North Eton Sugar Milling Company after leaving school, but became a career teacher with the Queensland Department of Education after 1904.

He taught at Ulam, near Rockhampton, Windorah West, Forsayth and Springsure, before being appointed headmaster at Yarraman Creek State School.

[1][2][3] Grimstone enlisted to fight during World War I, training at the Royal Military College, Duntroon, and being commissioned as a lieutenant.

[1][3][4] He was elected to the Legislative Assembly at a 1928 by-election, following the death of the incumbent member, Frederick Nott, defeating former MP and independent candidate, Henry Somerset, by 520 votes.

Labor leader William Forgan Smith expressed shock at Grimstone's sudden death, because it had been reported that his health was improving.