He was born in Eagle, Elgin County, Ontario.
Lang was first elected to the Ontario legislature in the 1914 provincial election as the Ontario Liberal Party Member of the Legislative Assembly for Cochrane.
While still a Liberal MLA, Lang attempted to move to federal politics in 1925 as a Labour candidate in Timiskaming South.
He was elected to the House of Commons of Canada on his next attempt, in the 1926 federal election in a straight contest against the Conservative incumbent and with the unofficial support of the Liberals who did not stand a candidate.
Though a Labour MP, Lang generally supported the federal Liberal government of William Lyon Mackenzie King and ran for re-election in the 1930 federal election as a Liberal-Labour candidate, with the full backing of the Liberal party, but was unsuccessful.