He is the son of Reine Gagné and Daniel Johnson Sr., who had been the Premier of Quebec from 1966 to his death in 1968, as the leader of the Union Nationale, a conservative political party.

Johnson immediately began his career in the business world and worked for Power Corporation of Canada from 1973 to 1981.

He ran for the 1983 Quebec Liberal Party leadership convention but finished third behind Pierre Paradis and winner Robert Bourassa.

Since 1998, Daniel Johnson has acted as senior counsel with the law firm McCarthy Tétrault LLP.

He is also a director of exp Global Inc., Bombardier Inc., The Great-West Life Assurance Company, The Investors Group, Ecopia Biosciences inc., and is Chairman of the Board of Victhom Human Bionics in Quebec City.