Since 2015, O'Brien has been the director of the Social Change Initiative, an international not-for-profit organisation based in Belfast, Northern Ireland, that supports activists and funders globally to secure progressive change, while also working to cement peace in Northern Ireland.
Prior to joining SCI, Martin worked for 11 years at the Atlantic Philanthropies, where he led the planning process for the conclusion of Atlantic’s programmatic grant making which worked to bring about lasting changes in the lives of disadvantaged and vulnerable people in Northern Ireland, the Republic of Ireland, South Africa and the United States by promoting peace-building and access to human rights.
As executive director of the CAJ, O'Brien helped to secure strong human rights provisions in the 1998 Good Friday Peace Agreement supported by most parties, that set forth a timetable and a structure to create a new power-sharing government in Northern Ireland.
O’Brien has brought concerns about the abuse of human rights in NI to international audiences, including the United Nations.
In May 1999, Notre Dame College presented him with an honorary Doctorate in recognition of his work to promote justice and peace in Northern Ireland.