Barry Robert O'Farrell (born 24 May 1959) is an Australian former politician who was Australia's High Commissioner to India and non-resident Ambassador to Bhutan from February 2020 to 30 June 2023. O'Farrell was the 43rd Premier of New South Wales and Minister for Western Sydney from 2011 to 2014. He was the Leader of the New South Wales Liberal Party from 2007 to 2014, and was a Member of the New South Wales Legislative Assembly from 1995 to 2015, representing Northcott until 1999 and representing Ku-ring-gai on the Upper North Shore of Sydney from 1999 to 2015. He was President and Independent Board Chair of Diabetes Australia, Chair of the Wests Tigers Rugby League Football Club and CEO of Racing Australia Ltd until taking up his role in India.

Born in Melbourne, his father's Army career saw O'Farrell and his family move around Australia, ending up in Darwin in the Northern Territory. In 1977 O'Farrell moved to Canberra to study at the Australian National University, where he gained a Bachelor of Arts. O'Farrell started his career as a graduate trainee in the Australian Public Service in Canberra. O'Farrell served as the State Director of the party in New South Wales from 1992 to 1995.

At the 1995 New South Wales election, O'Farrell was elected to the safe Liberal seat of Northcott in northern Sydney. Following the seat's abolition in the 1998 redistribution he secured selection for the equally safe seat of Ku-ring-gai in 1999 and held it until 2015. O'Farrell joined the Shadow Ministry in 1998 and served two periods as Deputy Leader (1999–2002 and 2003–2007). Following the Liberal-Nationals' defeat at the 2007 state election (their fourth in a row), O'Farrell challenged Peter Debnam for the Liberal leadership. Debnam withdrew from the contest on the day of the ballot and O'Farrell was elected unopposed as the Leader of the New South Wales Liberal Party and consequently as Leader of the Opposition. He became Premier in a landslide at the 2011 election, winning the largest majority government in New South Wales history.

On 16 April 2014, O'Farrell announced his intention to resign as party leader and NSW Premier as well as Minister for Western Sydney after misleading a New South Wales Independent Commission Against Corruption (ICAC) investigation. ICAC subsequently found "that there was no intention on Mr O'Farrell's part to mislead". He formally resigned on 17 April as Liberal Party leader and on 24 November 2014, O'Farrell announced his intention not to stand for re-election at the 2015 NSW election.

The youngest of three children, Barry Robert O'Farrell was born to Kevin and Mae O'Farrell in the Royal Women's Hospital, Melbourne, on 24 May 1959. He is descended from Irish immigrants who arrived in Victoria in the 1860s; and his paternal grandfather was an officer in the Victoria Police Force in Ballarat. The O'Farrells moved to Darwin during his adolescence and he finished his high school education at St John's College.

In 1977 O'Farrell began studying at the Australian National University in Canberra, residing at Ursula College. During his second year of study, he was elected President of the Ursula College Student Association. In 1980 he received a Bachelor of Arts (BA) in Australian history, politics and Aboriginal studies and has cited Professor Manning Clark and Don Baker as major influences for his continuing interest in Australian history.

After serving as a graduate trainee in the Department of Business and Consumer Affairs, in 1980 O'Farrell joined the Liberal Party and worked in the offices of two South Australian Senators, Tony Messner and Gordon Davidson.

When John Howard became Leader of the Opposition in 1985, his chief of staff, Gerard Henderson, hired O'Farrell as a Sydney-based adviser. In May 1988, O'Farrell was employed as Chief of Staff for Bruce Baird, a cabinet minister in the New South Wales government. Four years later, O'Farrell and Tony Abbott sought appointment as the State Director of the New South Wales Liberal Party. O'Farrell succeeded and he held this position until 1995.