William A. O'Neil (born June 6, 1927, died October 29, 2020) was a Canadian civil servant who served as Secretary-General of the International Maritime Organization and also served as Chancellor of the World Maritime University.

[1] In his early career, O'Neil worked at the Canadian Department of Transport.

[1] While Secretary-General, the IMO made several major decisions with a large impact on shipping.

[2] He oversaw the adoption of Annex VI of the MARPOL Convention in 1997 as well as the development of the International Safety Management Code.

[2] Following the September 11 attacks in 2001, he was also responsible for the IMO approach that led to the International Ship and Port Facility Security Code.