[3] Harris joined the Foreign and Commonwealth Office (FCO) in 1991 and was the Second Secretary at the UK delegation to the OCSE in Vienna from 1992 to 1996.

[4] He led the FCO's Pakistan and Afghanistan section from 1997 to 1998 and ran the UK's programme of technical assistance in the Russian Federation at the British Embassy in Moscow from 1999 to 2003.

[4] He then moved to the British Embassy in Kyiv where he was Consul General and Deputy Head of Mission from 2003 to 2008.

[4] Harris returned to London in 2008 where he was an adviser in the Cabinet Office on Afghanistan, Pakistan, Eastern Europe and Central Asia.

[4] Harris was named the new British Ambassador to Ukraine in July 2023 to succeed Melinda Simmons,[5][6] and assumed office in September of the same year.