Born in the Kuruman mission station in Bechuanaland (now in the Northern Cape province of South Africa), Moffat was the son of the missionary John Smith Moffat and grandson of the missionary Robert Moffat, who was the friend of King Mzilikazi and the father-in-law of David Livingstone.

He was elected to the Legislative Council in 1923 as member for Victoria and served as Minister of Mines and Works for the First Cabinet of Southern Rhodesia under Charles Coghlan.

Moffat was viewed as a conservative who believed that Rhodesia would eventually join the Union of South Africa.

He oversaw the purchase, for £2 million, of the British South Africa Company's remaining mineral rights in Southern Rhodesia.

[4] In the 1939 general election Moffat attempted to restart the Rhodesia Party but this met with failure.