Following Rhodri Morgan's decision to step down as the Member of Parliament for Cardiff West in order to concentrate on being the First Minister of Wales, Brennan was selected as the Labour candidate for the constituency and became the MP for Cardiff West at the 2001 general election. In 2002, he appeared in the House of Commons without a tie, as he favours a less formal dress code. After the 2005 general election, he was promoted to Tony Blair's government as an Assistant Government Whip. In June 2007, Blair's successor, Gordon Brown, appointed Brennan as Parliamentary Under-Secretary of State for Children, Young People and Families in the new Department for Children, Schools and Families, replacing Parmjit Dhanda. Brennan was replaced in this role by Lady Morgan following the government reshuffle in October 2008. He was moved to the Cabinet Office before being promoted in 2009, becoming the Minister of State for Further Education, Skills, Apprenticeships and Consumer Affairs, with responsibilities in both the Department for Education and the Department for Business, Innovation and Skills. Following the 2010 General Election, he continued this role in a Shadow Ministerial capacity before Ed Miliband's decision to appoint Brennan to the position of Shadow Minister for Schools. Brennan was made Shadow Minister for Trade, Investment, and Intellectual Property by Jeremy Corbyn in September 2015, with responsibility for, among others, low carbon business sectors, manufacturing, construction, trade, and intellectual property. He resigned from this position on 28 June 2016, following a motion of no confidence in Corbyn which was passed overwhelmingly by Labour MPs. He supported Owen Smith in the failed attempt to replace Jeremy Corbyn in the 2016 Labour Party leadership election. On 12 December 2019, Brennan was re-elected as the Member of Parliament for Cardiff West. Brennan supported Lisa Nandy in the 2020 Labour Party leadership election.
Pensions Bill/Allied Steel and Wire
In July 2002, the steel manufacturer Allied Steel and Wire entered receivership, and many of their employees were told they would not receive their full company pensions because of a fund shortfall. Mr Brennan, who had many former workers of Allied Steel & Wire as constituents, tabled an early day motion in the Commons in November calling for compensation, and threatened to table an amendment to the Pensions Bill if the government did not offer any help. After Brennan carried out his threat to table the amendment, The Independent newspaper reported that Tony Blair faced the "biggest backbench rebellion" of his career. Ultimately, Brennan was successful. The BBC said he was "instrumental in extracting the government's commitment to establish a £400 million fund to provide compensation for workers who lost their pensions when their firms went bankrupt".
Dress down Thursdays
In 2002 Kevin Brennan appeared in the House of Commons without a tie and called for Westminster to have "dress down" Thursdays, pointing out that Billy Bragg had complained Parliamentarians gave a "besuited image that's male, pale and stale". It provoked jeers from Conservative MPs. Michael Fabricant was so incensed that he made a point of order to the speaker. The Speaker, Michael Martin, agreed with Fabricant; and Brennan was forced to leave the chamber to retrieve a tie from his office.
Expenses
In 2009, Brennan came under scrutiny during the Expenses scandal for claiming questionable items, including a £450 television claimed for his London second home which was delivered to this family home in Cardiff. He claimed for bunk beds for his daughter while the expenses system was intended exclusively for items for the MPs' use. Brennan said he bought from businesses in his constituency but the items were for use in his second home, calling the story a "smear with no basis in fact".
Social Media Award
In 2010, Brennan became the first Member of Parliament to win the British Computer Society's Social Media MP of the year award, beating Nick Clegg and Jeremy Corbyn, who both finished as runners-up.
Guitars for prisoners
In 2014, Brennan led a campaign with musician Billy Bragg to lift a blanket ban on prisoners having access to guitars. They were backed in their campaign by musicians including Johnny Marr, David Gilmour and Richard Hawley. Brennnan held a Westminster Hall debate on the subject to try and get the government to overturn the ban, citing the importance and the efficacy of music as a means for the rehabilitation for prisoners. The Government agreed and prisoners can now have access to the instruments.
In 2016, following the murder of Jo Cox, the MP for Batley and Spen, Brennan put together the 'Friends of Jo Cox' to record a charity single to raise money for the Jo Cox Foundation which had been set up in her memory. The Friends of Jo Cox included the parliamentary rock band MP4, the House of Commons choir, MPs from other parties and a group of famous musicians including David Gray, KT Tunstall, Ricky Wilson and Steve Harley. The song was a cover of The Rolling Stones' "You Can't Always Get What You Want", with the Rolling Stones waiving their royalties for the Jo Cox Foundation. The single made the iTunes Top 10, and narrowly missed out on the top 100 UK Singles chart before Christmas Day. The single has raised more than £35,000.
