[1] He was educated at the Ontario Agricultural College in Guelph, and worked as a high school teacher, livestock sales owner, and operator-auctioneer.
[2][3] Riddell was first elected to the Ontario legislature in a by-election on March 16, 1973, defeating Progressive Conservative candidate Don Southcott by 2,968 votes in the riding of Huron.
[3] He expressed his concern that the 1988 Canada–United States Free Trade Agreement would be detrimental to farmers in Ontario, estimating that they could lose C$95 million, as well as lower food quality.
[15] He apologized to the legislative assembly in July 1985, after opining that Larry Grossman (who was Jewish and running to be leader of the Progressive Conservatives) would find it challenging to garner support in rural Ontario because "there still is a racist feeling" in those areas, but resisted calls to resign.
[20] After retiring from politics, Riddell intended to serve in a new ambassadorial post to instruct American lawmakers on the complexities of agriculture in the province, which was to be established by Premier David Peterson before the Liberals' unexpected defeat in the 1990 election.
[22] Two years later, his family established a scholarship in his honour for seniors in the Avon Maitland District School Board who demonstrate "academic and leadership skills in their community" and will study agriculture in Canada.