Garneau is a retired military officer, former astronaut, and engineer. Garneau was the first Canadian in space taking part in three flights aboard NASA Space shuttles in 1984, 1996 and 2000. He was appointed an Officer of the Order of Canada in 1984 in recognition of his role as the first Canadian astronaut. Garneau was the president of the Canadian Space Agency from 2001 to 2006, and in 2003 was installed as the ninth Chancellor of Carleton University in Ottawa.

He was elected to Parliament in October 2008 as a member of the Liberal Party for the Montreal riding of Westmount–Ville-Marie. He represented that riding until 2015 when it was redrawn. That year Garneau was elected to represent Notre-Dame-de-Grace–Westmount. Shortly thereafter Prime Minister Justin Trudeau named Garneau minister of transport. He held that post until January 2021, when he became minister of foreign affairs.

Garneau has been awarded the Canadian Forces Decoration for 12 years of honourable service with the Canadian Forces. Garneau is honoured with a high school named after him, Marc Garneau Collegiate Institute in Toronto and É.S.P. Marc-Garneau in Trenton, Ontario.