Career
Municipal politics
McLennan began his political career on the municipal level He ran for a seat to Edmonton City Council in the 1918 Edmonton municipal election. He ran for a second term in the 1920 Edmonton municipal election this time winning the second place seat.
McLennan resigned his municipal council seat in 1921 when he was elected to the Alberta Legislature.
Provincial politics
McLennan ran for a seat to the Alberta Legislature in the 1921 Alberta general election. He stood as a Liberal candidate in the electoral district of Edmonton.
He headed the polls taking first place in what would be a sweep by the Liberal slate among the 26 candidates. McLennan resigned his seat on October 15, 1925 to attempt to run for a seat in the Canadian House of Commons as a Liberal candidate in the 1925 Canadian federal election in the electoral district of Edmonton East.
He would be defeated by Conservative candidate Ambrose Bury finishing second in the three way race.