Martyn has lived in Abergavenny for 38 years. He sits on the Policy and Resources Committee. Alongside his local commitments, Martyn is also the Monmouthshire County Councillor for the Lansdown Ward. He represents the Town Council for the Borough Theatre and Black Mount Jazz.

He is the Cabinet Member for Education in Monmouthshire.  His interests include music and regularly attends the Black Mountains Jazz Club at the Melville Centre for the Arts in town, which is supported by the Town Council.