Dewar first entered politics in the early 1960s and was elected as Member of Parliament for Aberdeen South at the 1966 general election. After losing his seat in 1970, he served in the House of Commons again from 1978 until his death in 2000. He served as Secretary of State for Scotland in British Prime Minister Tony Blair's Cabinet from 1997 to 1999. Dewar was an advocate of Scottish devolution, successfully campaigning for a Scottish Parliament in the 1997 Scottish devolution referendum.