He was formerly a member of the Democratic Unionist Party (DUP), for which he successfully stood for election in 2004 to the European Parliament, succeeding Ian Paisley. He continued as a member of the European Parliament following his resignation from the DUP and his subsequent establishment of the TUV, but failed to retain his seat at the 2009 European parliamentary elections.
Allister was born in Crossgar in County Down. After attending Regent House Grammar School in Newtownards, Allister graduated with a Bachelor of Law with Honours in Constitutional Law from Queen's University of Belfast. In 1974 he unsuccessfully stood for the post of President of Queen's University Belfast Students' Union.
He was called to the Bar of Northern Ireland as a barrister in 1976, where he specialised in criminal law, and later called to the Senior Bar as a Queen's Counsel; he "took silk" in 2001.
Allister joined the DUP at its founding in 1971. He served as a European Parliament assistant to Ian Paisley from 1980 to 1982. In 1982 he was elected as a Member of the Northern Ireland Assembly at Stormont for North Antrim and served as the DUP Assembly Chief Whip. He was also the Vice-Chairman of Scrutiny Committee of Department of Finance and Personnel from October 1982 to June 1986. Outside the Stormont Assembly, he was a member of Newtownabbey Borough Council from 1985–87. In 1983, he had stood as a DUP candidate in the Westminster election for East Antrim. However he lost to Roy Beggs.
Following the signing of the Anglo-Irish Agreement in November 1985 by the Thatcher and FitzGerald governments, he was an opponent of the treaty. He was also a member of the Joint Unionist Working Party, a body set up by his party and the Ulster Unionist Party (UUP) to oversee the unionist campaign against the Agreement.
His departure from active politics in June 1987 followed a reported disagreement with Paisley over a voting pact with James Molyneaux's UUP. The situation resembled fellow unionist politician and barrister Robert McCartney's in the North Down constituency. McCartney was expelled from the UUP around the same time for not accepting the policy of the leadership.
Allister returned to run for the party's nomination for MEP in 2004. Allister was elected to the European Parliament for the DUP in the 2004 election. In March 2005 Allister was the victim of cybersquatting, when a domain advertised on the outside of his office was registered by the Ulster Young Unionist Council which preceded him. The domain read "Too slow Jim, vote Ulster Unionist"
On 27 March 2007, he resigned from the DUP because of the party's decision to enter into government with Sinn Féin. It was the second occasion on which he had resigned from the party
In late 2007, speculation began over Allister's political intentions, with it being suggested that a new Unionist political party was imminent. It was claimed on 10 October 2007 that he had been approached by the United Kingdom Independence Party, but he proceeded to found the Traditional Unionist Voice party on 7 December 2007.
In the 2009 European elections, he gained only 13.5% of the first preference vote, standing as a TUV candidate and lost his European Parliament seat on the second count.
He intimated that he might stand as a candidate for the Westminster Parliamentary election in North Antrim. According to the European election result in North Antrim, Allister stood a good chance of winning the seat, which would have been a tremendous loss to the DUP – historically the DUP's safest seat and the seat of DUP founder and former party leader Ian Paisley.
In the 2010 General Election, Allister finished second in North Antrim, with 7,114 votes to the DUP's Ian Paisley Junior who polled 19,672 votes. His TUV party polled some 26,300 votes throughout Northern Ireland, a drop of almost two-thirds in their level of support at the European election in 2009. In the 2011 Stormont Election, he was elected MLA of North Antrim, claiming the 6th seat.
In August 2012 Allister called the Parades Commission "little Hitlers" when they placed restrictions on a loyalist parade.
Allister holds conservative views on social policy and is a supporter of the evangelical creationist lobby group, the Caleb Foundation.