Brendan has been actively involved in peacebuilding in Northern Ireland since 1974. After years of peace activism, he left his career in social work in 1992 to commit himself full-time to the development of mediation as a method of peace-building. He was responsible for providing leadership for the growth and evolution of an indigenous mediation field, using culturally sensitive and contextually nuanced methodology. He worked as a mediator primarily through the development of local practice: at street level; across peace lines in Northern Ireland; within circles of civic leadership; among political leaders; with paramilitaries, inside and outside of prisons; with institutions of state; with Government and, at times, in partnership with outside third parties from the international community.
From 1992 to 2008, Brendan was the Director of Mediation Northern Ireland, one of the foremost national mediation organisations working throughout the troubles. During this time, Brendan played a significant role in police reform regarding organisational culture, change management and community policing. He acted as Mediation Advisor to the Parades Commission in Northern Ireland, advising Commissioners on the management and resolution of disputes over parades across Northern Ireland; training and managing a team of mediators; and mediating in a range of disputed parades. In 2003 he became a Neighbourhood Renewal Advisor for England, working on racial tension, gang violence and social cohesion. As Victims Commissioner between 2008 and 2012, he was a principal advisor to the Government concerning the needs of victims and survivors of the conflict in Northern Ireland and worked with families and groups representing those with enduring trauma and distress.