Antoniazzi contested the regional seat of Mid and West Wales in the 2016 National Assembly for Wales election.
At the snap 2017 general election, Antoniazzi was elected as MP for Gower with 49.9% of the vote and a majority of 3,269.[10][11][12] She delivered her maiden speech on 29 June 2017. In her speech she outlined how Italian immigration had shaped cafe culture in Wales and the UK.[13]
In June 2019, Antoniazzi urged ministers to allow the use of medical cannabis by "all who need it", citing the case of 12-year-old Billy Caldwell whose epilepsy was alleviated through use of the drug.[14]
At the 2019 general election, Antoniazzi was re-elected as MP for Gower with a decreased vote share of 45.4% and a decreased majority of 1,837.[17][18][19]
At the 2024 general election, Antoniazzi was re-elected as MP for Gower with a decreased vote share of 43.4%. However, Antoniazzi won with an increased vote count of 11,567 and a widened majority of 24.5%.[21]
On 13 June 2018, Antoniazzi and five other Labour MPs resigned their roles as frontbenchers for the Labour Party in protest at Labour's Brexit position. 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 including Antoniazzi resigned and voted in favour of the EEA.[23][24]
In the series of Parliamentary votes on Brexit in March 2019, Antoniazzi voted against the Labour Party whip and in favour of an amendment tabled by members of The Independent Group for a second public vote.[25]
In October 2021, Antoniazzi criticised the LGBT charity Stonewall, stating the Welsh government had promoted an "ideological culture" and were "dictated to by Stonewall".[26]
In January 2022, Antoniazzi and four other Labour delegates to the Parliamentary Assembly of the Council of Europe tabled ten amendments[27] to Resolution 2417, "Combating rising hate against LGBTI people in Europe".[28] The amendments sought to include the word "sex" alongside gender identity, de-conflate the situation in the UK from Hungary, Poland, Russia and Turkey, and remove references to alleged anti-LGBTI movements in the UK. The delegates were criticised by Pink News for removing references to anti-LGBTI attacks in the UK, a condemnation of anti-trans movements and a call to withdraw funding from anti-LGBTI groups or authorities; in turn the delegates were defended by Debbie Hayton, a gender-critical activist, for protesting the removal of sex-essentialist language she considered important for non-trans women.[29][30]
In July 2022, Antoniazzi submitted an application on behalf of the gender critical group Labour Women's Declaration for them to have a stand at the party's annual conference in Liverpool, which was subsequently denied. In response, Antoniazzi pushed for the group's public conference, chaired by her, to be given an official listing.[31][32]
