He was inducted into the Congress by Rajiv Gandhi, who was his friend from school and was first elected to the Lok Sabha in 1980. In 1984, he resigned from Parliament and from Congress as a protest against the Army action during Operation Blue Star. Subsequently, he joined the Shiromani Akali Dal was elected to the state legislature from Talwandi Sabo and became a minister in the state government for Agriculture, Forest, Development and Panchayats. In 1992 he broke away from the Akali Dal and formed a splinter group named Shiromani Akali Dal which later merged with the Congress in 1998 after Sonia Gandhi took over the reign of the party. He was defeated by Prof Prem Singh Chandumajra from Patiala Constituency in 1998 by a margin of 33,251 votes. He served as the President of Punjab Pradesh Congress Committee on three occasions from 1999 to 2002, 2010 to 2013 and 2015 to 2017, he also became Chief Minister of Punjab in 2002 and continued until 2007. In September 2008, a special committee of Punjab Vidhan Sabha, during the tenure of a government led by Akali Dal-Bharatiya Janata Party, expelled him on the count of regularities in the transfer of land related to the Amritsar Improvement Trust. In 2010, the Supreme Court of India held his expulsion unconstitutional on the grounds that it was excessive and unconstitutional. He was appointed as chairman of Punjab Congress Campaign Committee in 2008. Captain Amarinder Singh is also a Permanent Invitee to the Congress Working Committee since 2013. He defeated senior BJP leader Arun Jaitley by a margin of more than 102,000 votes in 2014 general elections. He has been a member of the Punjab Vidhan Sabha for five terms representing Patiala thrice, Samana and Talwandi Sabo once each. On 27 November 2015, Amarinder Singh was appointed President of Punjab Congress in the run up to Punjab elections slated for 2017. On 11 March 2017 Congress Party won the State Assembly Elections under his leadership. Amarinder Singh was sworn in as the 26th Chief Minister of Punjab on 16 March 2017 at Punjab Raj Bhavan, Chandigarh. The oath of office was administered by the Punjab governor, V.P. Singh Badnore. He was appointed president of the Jat Mahasabha in 2013.
Books
He has also written books on war and Sikh history which include A Ridge Too Far, Lest We Forget, The Last Sunset: Rise and Fall of Lahore Durbar and The Sikhs in Britain: 150 years of Photographs. Among his most recent works are Honour and Fidelity: India's Military Contribution to the Great War1914 to 1918 released in Chandigarh on 6 December 2014, and The Monsoon War: Young Officers Reminisce – 1965 India-Pakistan War- which contains his memoirs of the 1965 Indo-Pak war.
Awards and recognitions
The author Khushwant Singh released a biographic book titled, Captain Amarinder Singh: The People’s Maharaja in 2017.