He served in the Legislative Assembly of Manitoba from 1899 to 1915 as a member of the Conservative Party.

He later moved to Stonewall, Manitoba where he was a lumber merchant and also owned a hotel.

The Conservatives won a majority government, and Riley served as a backbench supporter of the administrations led by the Hugh John Macdonald and Rodmond Roblin.

In the 1914 campaign, he defeated Liberal candidate Arthur Lobb by fifty-nine votes.

[1] The Roblin administration was forced to resign in 1915 amid a serious corruption scandal.