First elected as a Liberal Member of Parliament for the riding of Inverness--Richmond in 1953, MacEachen served under Prime Ministers St. Laurent and Pearson. He took on a senior role in Pierre Trudeau's Ministry, and in 1977 was named Canada's first Deputy Prime Minister, a post he held until Trudeau's retirement in 1984. MacEachen spent the latter years of his political career as Liberal leader in the Senate, where he sat until his mandatory retirement at the age of 75 in 1996.