On 8 June 2017, McMorrin was elected as the Member of Parliament for
Cardiff North. Shortly after becoming an MP, McMorrin asked leader of the House of Commons,
Andrea Leadsom, for an urgent debate about the 1,100 Tesco job losses in Cardiff North. McMorrin strongly opposed the decision, and asked for it to be reviewed. McMorrin was successful in gaining an urgent debate in the House of Commons on 19 July 2017, and in her speech said she wished to "highlight the way in which Tesco has acted; secondly, describe the human impact of these actions; and finally, explore how we respond to these things and the next steps.". McMorrin is a member of the
Environmental Audit Select Committee and joined the
Welsh Affairs Select Committee on 24 October 2017 following criticism of both an unfilled committee and an all-male lineup. McMorrin served as the Parliamentary Private Secretary (PPS) to
Barry Gardiner, Shadow Secretary of State for International Trade, until her resignation in 2018. On 13 June 2018, McMorrin and five other Labour MPs resigned their roles as frontbenchers for the Labour Party in protest at Labour's
Brexit position. Leader
Jeremy Corbyn had instructed his MPs to abstain in a vote which Britain would remain in the single market by joining the
European Economic Area (EEA). The MPs resigned and voted in favour of the EEA. McMorrin voted against the Labour Party whip and in favour of an amendment tabled by members of
The Independent Group for a second public vote on EU membership in March 2019. On 12 December 2019, McMorrin was re-elected as the Member of Parliament for
Cardiff North with a slightly increased majority of 6,982. Upon Keir Starmer's election as Labour leader in April 2020, she was appointed as a Shadow Minister for International Development. In a minor reshuffle in May 2021, McMorrin succeeded
Peter Kyle as the Shadow Minister for Victims and Youth Justice. At the
2024 United Kingdom general election, McMorrin was re-elected, following boundary changes to the constituency, with a reduced majority. She is a member of the
Fabian Society. ==Personal life==