The second son of William Rankin, colliery manager, and his wife Jane, née Anderson, he was educated at Galston Public School and Kilmarnock Academy. Colin Rankin accompanied his family to Queensland when his father became manager of Queensland Collieries Co. Ltd. at Howard (near Maryborough) in 1884. Rankin joined its staff and from 1886 the Queensland Defence Force. By 1890 he was assistant company manager, grew sugar at Tigh-na-Bienne at Isis, Queensland (near Bundaberg, north of Howard), and became a clerk and valuator with the Isis Divisional Board (1890–1899).