He was the Assistant Agricultural Representative in Hastings and Essex Counties, then the Assistant Manager of the Ontario Stockyards.
At home, he raised cattle and sheep on a farm near Dashwood, Ontario, even while working as a teacher at the South Huron District High School.
He owned and operated the Hensall Livestock Sales Barn and worked as an auctioneer jointly with his brother Doug.
After becoming the Ontario Minister of Agriculture and Food in 1985, he introduced the Ontario Family Farm Interest Rate Reduction program and formed an Agriculture Caucus Committee of rural MPPs.
For his efforts to sustain and advance agriculture, Riddell was elected to the Ontario Agriculture Hall of Fame in June 2017.
A service for Riddell took place on January 27, 2024.