Onley attended school in Scarborough and graduated from the University of Toronto in 1975 with an honours BA in political science. He attended the University of Windsor law school but ultimately chose a career in broadcasting, becoming the first newscaster in Canada with a visible disability.
During Onley's 22-year career with Citytv, he held positions as news anchor, host, producer, science and technology specialist and weathercaster. He embarked on several writing projects at the same time, and was nominated for the Periodical Distributors of Canada Book of the Year (1982) for his novel Shuttle. Throughout his career he has contributed to television, radio and publications in various capacities, focusing on topics such as technology, science and faith.
In addition to his career in media, Onley worked to improve accessibility for the disabled in public places. He has chaired the Government of Ontario's Accessibility Standards Advisory Council and served on the SkyDome Accessibility Council and the Air Canada Centre Accessibility Committee. He has assisted the Muki Baum Association, the Ontario March of Dimes, Variety Village, the Canadian Foundation for Physically Disabled Persons, and the Centre for Independent Living in Toronto. Onley was appointed chair of the Accessibility Standards Advisory Council to the Ontario Minister of Community and Social Services in 2005.
Onley's dedication to advocacy has been recognized by numerous groups. He has been given the King Clancy Award, the Courage to Come Back Award and the Positive Impact Award. Onley has been inducted into the Scarborough Walk of Fame and the Terry Fox Hall of Fame, and he has received an honorary Doctor of Laws degree from Canada Christian College.