[6] Before entering politics, O'Hara worked as a community worker in loyalist areas, delivered European Union peace funding programmes and managed health initiatives for the Rainbow Project, Ireland's biggest LGBT organisation.

[2] He was the Green Party candidate for Belfast North at the 2016 Northern Ireland Assembly election, where he was eliminated on the seventh count with 796 first preference votes (2.18%).

[16][17] O'Hara became the leader of the Green Party Northern Ireland on 15 August 2022, following a leadership election in which he was the only candidate.

[20] In March 2024, O'Hara was announced as the Green Party candidate at the 2024 Seanad by-election and was elected unopposed.

During the first wave of the COVID-19 pandemic, O'Hara led a group of over 70 volunteers who set up a cross community soup-kitchen to deliver over 17,000 meals to vulnerable people across North and West Belfast.