Theodore was born in Port Adelaide, South Australia, to parents Basil Theodore and his wife Annie (née Tanner). His brother was Ted Theodore, the former Premier of Queensland and Treasurer of Australia. Arriving in Queensland in 1915 after working the goldfields in New South Wales and Western Australia, he was a sugar grower in Tully by 1923 becoming the Director and Chairman of the Tully sugar mill. In 1950 he was a banana farmer in Tully.
