Donaldson is known for his opposition to UUP leader David Trimble's support of the Good Friday Agreement during the Northern Ireland peace process, especially from 1998 to 2003.

[9][10] In March 2024, he stepped down as leader of the DUP, having been charged with rape and historical sexual offences, triggering a leadership election.

[3] In October 1985, at the age of 22, following the death of Raymond McCullough, Donaldson was elected with a large majority in a by-election to the Northern Ireland Assembly to represent South Down.

[23] In April 1986, Donaldson took part in a unionist demonstration attempting to blockade a conference of the Ulster Teachers' Union held in Newcastle, County Down, in protest at the Anglo-Irish Agreement.

[23] In June that year, after Secretary of State for Northern Ireland, Tom King, ordered the dissolution the Assembly, Donaldson was one of 21 unionist representatives who refused to leave the chamber at Stormont and was eventually physically removed from the building by the RUC.

Donaldson, by that time serving as Assistant Grand Master of the Orange Order, was a prominent figure in the ongoing Drumcree conflict over a yearly loyalist parade in the town of Portadown.

[30] He rejected some of the arrangements, notably the lack of a link between Sinn Féin's admittance to government and IRA decommissioning.

The council, however, backed Trimble's leadership, and on 23 June 2003, along with fellow MPs David Burnside and Martin Smyth, Donaldson resigned the Ulster Unionist whip at Westminster.

[30][35] Donaldson was returned to the House of Commons in the 2005 UK general election and, in 2007, he was appointed to the Privy Council of the United Kingdom, entitling him to the honorific style of The Right Honourable.

[36] In July 2009, The Daily Telegraph reported that Donaldson had repaid £555 claimed for pay-to-view films in overnight hotel stays.

The newspaper claimed "hotel sources confirmed that films he put on his expenses during 2004 and 2005 were in the highest price category offered to guests, covering the latest blockbusters and adult movies", although no evidence was offered and Donaldson issued an official statement denying watching any content of an adult or pornographic nature.

[40] On 3 May 2021, exactly 100 years after Northern Ireland was effectively established,[41] Donaldson declared his candidacy for the leadership of the DUP to replace Arlene Foster.

[42] Poots resigned after only 21 days as leader, having faced an internal revolt against his decision to proceed without delay to nominate Paul Givan as First Minister, after Sinn Féin had reached an agreement with the Westminster government about an Irish Language Act.

[44] On 21 June, Donaldson declared his candidacy for the leadership of the DUP to replace Poots,[21] pledging to make the Northern Ireland Protocol his main priority.

[51] On 29 March 2024, Donaldson resigned as DUP leader after being charged with rape and other historical sexual allegations, which he said he would "strenuously contest".

Social Democratic and Labour Party (SDLP) deputy leader Alasdair McDonnell demanded an apology from Donaldson and a retraction of his claim that Catholics owed allegiance in the first instance to the Pope and the Holy See.

[1] On 28 March 2024, Donaldson was arrested by the Police Service of Northern Ireland (PSNI) and charged with rape and a number of other sexual offences.

The Orange Order[64] and the DUP suspended his memberships in March 2024 pending the outcome of the judicial process, as required by their rules.

[11][12] As Donaldson and his wife are co-defendants they were initially bailed to separate properties, and thus she returned to their marital home in Dromore while he flew to London to reside in a flat in Greenwich.

[65] In response to what it deemed "unhelpful speculation" by some members of the public and media outlets (in regards to his legal issues being used to influence his decision to restore the Executive in January 2024), the PSNI released a statement clarifying that they first received a complaint that resulted in Donaldson's arrest in early March 2024.

[70] On 3 July 2024, Donaldson and his wife again appeared before Newry Magistrates' Court, where prosecution lawyers asserted that there was a prima facie case to answer and both defendants had failed to offer any contrary submissions.

[71][72] On 10 September 2024, Donaldson and his wife both entered not guilty pleas to all charges during an arraignment hearing at Newry Crown Court.