David Cecil Williams is a Canadian physician and public servant who served as Chief Medical Officer of Health for the province of Ontario from 2015 to 2021.

He served as acting Chief Medical Officer of Health for the province from 2007 to 2009 and again from 2015 to 2016 until taking the position permanently.

[2] Williams initially worked as a general practitioner and anesthetist in Sioux Lookout, Ontario and served on an international mission in a hospital setting to Tansen, Nepal.

His promoted and suggested methods to health care providers in the province involve harm reduction[4] and the extended use of opioid replacement therapy with drugs such as suboxone.

[7][8] In November 2020, Williams was scheduled to retire from his position, but was convinced to stay on by Premier Doug Ford[9] until June 25, 2021 when he was succeeded by Kieran Moore.