Born in Toronto, David Smith was educated in Toronto, Victoria and Peterborough before attending university in Ottawa. Senator Smith earned a B.A. in Political Science from Carleton University in 1964 and an LL.B from Queen's University in 1970. He was called to the Bar in Ontario in 1972. Throughout his legal career, Senator Smith became a leading practitioner in municipal, administrative and regulatory law.

David Smith became an active member of the Liberal Party in the 1960s, holding such positions as National President of the Young Liberals. In addition, he served as National Youth Director and assistant to Keith Davey, who was the National Liberal Party director.  David also served as Executive Assistant to the Hon. Walter Gordon and the Hon. John Turner during the administration of Prime Minister Lester B. Pearson.

In 1972, David Smith was elected to the Toronto City Council and re-elected in 1974 and 1976. In 1976 he was also appointed President of Toronto City Council and Deputy Mayor of Toronto. From 1980 to 1984, Senator Smith sat in the House of Commons as Member of Parliament for the riding of Don Valley East and also served in Prime Minister Trudeau's cabinet as Minister of Small Business and Tourism.

After the 1984 election, David Smith returned to the practice of law in Toronto, and he became Chairman of the law firm Fraser & Beatty in January of 1994. He also continued to play an active political role, chairing election campaigns for Prime Minister Chrétien in the 1993, 1997 and 2000 elections.

At the time of his appointment to the Senate in June 2002, Senator Smith was Chairman of Fraser Milner Casgrain LLP, one of Canada's oldest and largest law firms, with over 550 lawyers in seven cities. Senator Smith had also served as Chairman of FMC's predecessor firms, both Fraser & Beatty and Fraser Milner.

In addition to having sat on several corporate boards, Senator Smith has lent his time to numerous voluntary and philanthropic organizations. He has sat on the Board of Governors of Exhibition Place, as well as on the boards of the Salvation Army, Toronto General Hospital, Mount Sinai Hospital and George Brown College. He has served as Chairman of the Retinitis Pigmentosa Foundation and as Vice Chairman of the O'Keefe Centre for the Performing Arts. Currently, he is on the board of the Corporation of Massey Hall and Roy Thomson Hall.

Senator Smith and his wife, Heather, have raised three children: Alexander, Kathleen and Laura. His wife, Heather, is Chief Justice of The Superior Court of Ontario and has served on the bench since 1983.