Donald James Johnston (born 1936) was first elected to the Canadian House of Commons in a 1978 by-election representing Westmount in Montreal. A Liberal, Johnston served in the cabinet of Prime Minister Pierre Trudeau from 1980 to 1984 variously as president of the Treasury Board as well as several other positions. When Trudeau announced his retirement in 1984, Johnston ran in that year's Liberal leadership convention, coming in third behind John Turner and Jean Chrétien. Johnston served as minister of justice and attorney-general in the short-lived Turner government until its defeat in the 1984 federal election

In opposition Johnston and Turner split over the issue of the Canada-U.S. Free Trade Agreement with Johnston supporting free trade and Turner passionately opposing it. On January 18, 1988, Johnston resigned from the Liberal caucus to sit as an independent liberal until retiring from Parliament when the 1988 general election was called. Johnston returned to the Liberal fold in 1990, after Turner's resignation as leader, and served two terms as president of the Liberal Party of Canada from 1990 to 1994, seeing the party through its victory in the 1993 general election. In 1996 the government of Prime Minister Jean Chrétien proposed Johnston for the position of secretary-general of the OECD. Johnston was elected to the post by the organization's member governments and took up the position on June 1, 1996, and still holds it as of 2005.