Sir Malcolm was one of only five ministers to serve for 18 years, throughout the whole Prime Ministerships of both Margaret Thatcher and John Major. This was the longest, uninterrupted, ministerial service in the United Kingdom since Lord Palmerston in the early 19th century.  In 1997 he was knighted in recognition of his public service.

From 1979, he served as Parliamentary Under Secretary of State in the Scottish Office and the Foreign and Commonwealth Office, becoming Minister of State in 1983. He joined the Cabinet in 1986 as Secretary of State for Scotland, and in 1990 became Secretary of State for Transport.

His most notable roles were from 1992 as Secretary of State for Defence and from 1995-97 as Foreign Secretary.

Sir Malcolm was re-elected as a Member of Parliament in May 2005 for Kensington and Chelsea and remained in Parliament until 2015.He served as UK representative on the Commonwealth Eminent Persons Group 2010-2011 and as Chairman of the Intelligence and Security Committee of Parliament, which provides oversight of the UK's intelligence agencies, MI6,MI5 and GCHQ, from 2010 until 2015.

He is currently a member of the OSCE's Eminent Persons Group, which has reported on relations between Russia and the West. He also serves on the Board of the Nuclear Threat Initiative in Washington DC.

He has been appointed a Visiting Professor at King's College, London and is a Senior Associate Fellow of the Royal United Services Institute (RUSI).