As a teenager, Foster was on a school bus that was bombed by the IRA, the vehicle targeted because its driver was a soldier in the Ulster Defence Regiment (UDR).

[17] At the 1991 annual conference of the UUP's youth wing, the Ulster Young Unionist Council (UYUC), during abortive talks between the constitutional political parties in Northern Ireland initiated by Secretary of State Peter Brooke, she seconded a motion opposing devolved government in Northern Ireland, instead calling for the province to be more closely integrated with the rest of the United Kingdom.

[18] Following the 1993 local elections in Northern Ireland, she wrote a letter to Ulster Review, the current affairs magazine of the UYUC, expressing opposition to power-sharing arrangements with the Social Democratic and Labour Party (SDLP) on local councils where unionists had a majority, arguing that because the SDLP were a nationalist party who wanted to the see the "demise" of Northern Ireland who had "no desire to be full citizens of the United Kingdom" they "should therefore be denied the perks of this citizenship".

[20] In 2004, Foster resigned from the UUP and joined the Democratic Unionist Party (DUP), together with fellow Assembly members Jeffrey Donaldson and Norah Beare.

[citation needed] On 11 January 2010, she assumed the duties of the First Minister of Northern Ireland, as Peter Robinson stepped aside for a planned period of up to six weeks.

[27] In September 2007, a privately financed proposal for a new Giant's Causeway centre was given preliminary approval by Foster in her role as Northern Ireland Environment Minister.

[29] On 29 January 2008, Foster announced that she had decided against Sweeney's proposal for a £21 million visitors' centre on a protected greenfield site, reversing her earlier position of "being minded" to approve it.

[33] As the minister responsible for energy policy in June 2012, Foster criticised the Co-operative Group over the showing of a documentary opposing fracking, saying: "I find your claim that you take 'ethics to the next level' hard to reconcile with your demonstrable support for a film which presents a wholly one-sided and partial approach to the debate about hydraulic fracturing.

"[34] She successfully liaised with UK ministers, such as Secretary of State for Northern Ireland Theresa Villiers MP, to restore HMS Caroline in Belfast.

In March 2014, Foster called for an apology for what she described as "deeply insulting" language" in a comment made by fellow MLA Anna Lo of the Alliance Party of Northern Ireland.

The former UVF member who was responsible for two sectarian murders during The Troubles stated that he had "no regrets in terms of my past because I believe that I contributed to preventing a united Ireland."

"[36][37][better source needed] In January 2016, as she was poised to become First Minister, Foster stated that she would not be travelling to Dublin for the official centenary celebrations of the 1916 uprising against British rule, describing the rising as "an attack on democracy".

[42] Foster stated that, despite her opposition to same-sex marriage, she valued the contribution of the LGBT community in Northern Ireland and requested that differing views be respected.

The reduction of sales and purchase taxes, such as Air Passenger Duty was typically part of her wider experience of stimulating business at DETI.

[43] Fighting the cause of private enterprise has been an important issue for Foster: mobile phone companies and saving Bombardier jobs brought investment of £500 million, while public sector employment has declined.

[44] In December 2016, Foster faced criticism and controversy after a whistleblower revealed that the Renewable Heat Incentive scheme overspent by £400m, a failure which has been nicknamed the Cash for Ash scandal.

She faced strong criticism after it was claimed that she personally campaigned to keep the scheme open, even when senior civil servants warned of the overspend and the Minister responsible, Jonathan Bell, planned on closing it.

James Brokenshire, the Secretary of State for Northern Ireland, assumed the powers of the Executive and called for a snap election scheduled for 2 March.

[56] With no party having received an outright majority in the UK Parliament, the DUP entered into a confidence and supply agreement to support the government led by the Conservative Prime Minister Theresa May.

[57] Following a Brexit breakthrough on 8 December 2017, Foster broadly welcomed the deal to progress talks, stating that she was "pleased" to see changes which meant there is "no red line down the Irish Sea".

[61][62] After the Executive was not restored by the deadline, abortion was decriminalised automatically; in December 2019 the British Government passed regulations legalising same-sex marriage and opposite-sex civil partnerships on 13 January 2020.

[66][67] In a Daily Telegraph op-ed she maintained that the Northern Ireland Protocol (NIP) had "fundamental flaws" and suggested, in light of the COVID vaccine dispute, that in order to "protect the UK internal market by all legislative means necessary including triggering Article 16, Boris Johnson must now back up those words with tangible actions that protect the integrity of the whole of the United Kingdom.

[69] The group was joined by Nobel Peace Prize winner David Trimble on 24 February, as he wrote a scathing open letter to Boris Johnson prior to the commencement of proceedings.

Foster was part of discussions involving deputy First Minister Michelle O'Neill, Chancellor of the Duchy of Lancaster Michael Gove and Vice-President of the European Commission Maroš Šefčovič.

[80] In August 2022, Foster endorsed Liz Truss in the Conservative Party leadership election as the best potential Prime Minister to counter “threats to the Union”.

[84] In November 2022, a video in which a woman shouted a pro-IRA chant while posing alongside Foster was condemned by politicians from the DUP, UUP, Alliance Party and SDLP, with Sinn Féin Vice President Michelle O'Neill saying it was "wrong".

[92] In response to the 2024 United Kingdom riots in Northern Ireland, Foster rejected what she called the "labelling" of some white working-class people in Belfast "as Nazis".

[94] In October 2024, it was reported that Foster has been advertising herself for hire through a public speaking agency as a renewable energy expert at a cost of more than £10,000 a day despite her involvement in the RHI scandal.

[95] Speaking to Michael Gove on a Radio 4 podcast in October 2024, Foster confirmed that a row over conversion therapy was the "straw that broke the camel's back", when it came to her being ousted as leader of the DUP.

[97] In January 2025, Foster was one of seven MPs and peers from Northern Ireland, along with more than 160 other parliamentarians, to call for the England men's cricket team to boycott a match against Afghanistan due to the Taliban regime's oppression of women.