O'Brien was elected as a TD in the November 2019 Dáil by-election for Dublin Fingal. He was elected to Fingal County Council in the 2019 local elections. He has worked in research, policy and advocacy on minority access issues to social protection and homelessness. He is a qualified project manager and formerly worked for the Immigrant Council of Ireland.

Dublin Fingal needs a Green voice and a champion for human rights and equality. I have considerable experience in this area and will work hard for the people of Dublin Fingal.

Infrastructural deficits are a key issue for the constituency - lack of school places, inadequate public transport, non-existent cycle lanes, shortages in garda numbers all show that investment in public services have not increased in line with the population increase in the constituency.

I would like to inject a greater sense of urgency into the homelessness crisis. It has been the greatest failing of this government and I would work to improve the lives of the 3,000 children who currently find themselves without a home.