She was the Fianna Fáil junior Spokesperson for Older People and Chair of Oireachtas Cross Party group on Dementia. She had been a member of Waterford City and County Council from 2014 to 2016, before her election to the Dáil in 2016.[3]
Butler was opposed to the legalisation of abortion in Ireland. She called for a No vote in the 2018 referendum on abortion, and co-organised an event calling for a No vote.[4]
Butler put forward a bill in 2018 with the aim of banning tattoos and intimate piercings for people under the age of eighteen; this bill lapsed with the dissolution of the Dáil.[5][6]
Former Fianna Fáil TD Brendan Kenneallycanvassed for Butler during the 2016 general election campaign, at which she was first elected to the Dáil.[9] Bill Kenneally, a cousin of Kenneally's, was convicted of 1980s sexual abuse of boys, and Kenneally had previously acknowledged that he had been aware of his cousin's crimes before his sentencing to 14 years imprisonment.[10] Butler received criticism for Kenneally's involvement in her 2016 campaign.[9] However, four years later, she again had Keneally canvass for her ahead of the 2020 general election.[9] Kenneally's canvassing for Mary Butler in 2020 became public knowledge when it emerged that he had visited the homes of some of those who had been abused to seek their votes.[9]
It also emerged that Butler was renting her constituency office from Kenneally, and when it did so, she stated in an interview that she would move elsewhere and did so in early 2020.[9]