Hourigan joined the Green Party in 2011. She was elected to represent
Cabra-
Glasnevin local electoral area on
Dublin City Council at the
2019 local elections. She is the Green Party's Spokesperson for Finance and Health. Hourigan helped to establish the Irish Pedestrian Network born out of Dublin Blockers, a social media campaign she started in 2018 highlighting the issues pedestrians in Central Dublin were facing. Within this network, she organised an activist group, Streets are for People. At the
2020 general election, Hourigan was elected as a TD for
Dublin Central. Darcy Lonergan was then co-opted to Hourigan's seat on Dublin City Council. On 22 July 2020, Hourigan was amongst several prominent members of the Green Party who formed the "Just Transition Greens", an affiliate group within the party with a
green left/
eco-socialist outlook, who have the objective of pressuring the party towards more hardline policies based on the concept of a
Just Transition. On 30 July 2020, Hourigan resigned as
party whip of the
Green Party, but did not leave the party after voting against the
Government twice on amendments to the Residential Tenancies Bill. She was later sanctioned by
party leader Eamon Ryan by having her speaking rights withdrawn for two months. In December 2020 Hourigan, alongside fellow Green TD
Patrick Costello, spoke out against the entry of Ireland into the
Comprehensive Economic and Trade Agreement (CETA), a trade agreement between Canada and members of the EU, due to fears about the proposed "Investment court system". The investment court system is designed to act as a method of solving business disputes between investors and participating countries. Hourigan and Costello argued that the court system would allow Canadians investing in Ireland to sue the state if the state impeded their profits, such as with environmentalist laws, and this was a major threat to Ireland's sovereignty. On 17 May 2022 Costello and Hourigan were both suspended from the Green Party for six months after they voted against the government on a motion calling for the new
National Maternity Hospital to be built on land wholly owned by the state. Before the vote, Hourigan explained her rationale by saying she could not support the government's decision to approve plans to move the National Maternity Hospital from Holles Street to the St Vincent's Hospital campus due to concerns over the governance and ethos at the new facility, which is to be built on a site ultimately leased from the
Catholic Church, and with fears in some quarters that potential lingering religious influence could mean abortions or fertility treatment would not be allowed to take place at the new hospital. The government coalition parties (
Fine Gael,
Fianna Fáil and the Greens) had been whipped to abstain on the motion. On 7 March 2023, Hourigan criticised the government for its decision to end the eviction ban, calling the decision "heartless". Hourigan also spoke out against Green Party leader Eamon Ryan, saying that he did not speak to the party's policies. Senator and Green Party Chair
Pauline O'Reilly rebuked Hourigan's remarks and said that it was "clear Neasa didn't have all the facts". On 22 March 2023 Hourigan was suspended from the Green Parliamentary Party for fifteen months and removed from her committee position for voting against the government on an amendment to a
Sinn Féin motion calling for the extension of the eviction ban. On 14 July 2024, Hourigan was
narrowly defeated by Senator
Róisín Garvey in an election to replace
Catherine Martin as
deputy leader of the Green Party. At the
2024 general election, Hourigan received 1,952
first preference votes, the seventh highest in the 4-seater
Dublin Central constituency. She was eliminated on the 7th count, and lost her seat. ==Political views==