Fr. John Harris was born in Limerick, Ireland. He was professed as a Dominican in 1982 and ordained a priest in 1988. He has taught systematic theology and moral theology in the Irish Dominican Studium and received his BA in philosophy and politics from University College Dublin.

In 2004 he received a doctorate from the Angelicum in Rome having written his doctorate under the direction of Fr. Wojciech Giertych OP (now theologian to the papal household). The title of the thesis was "Ethics in Constitutional Law - A Theological reflection on the Preamble to the Irish Constitution".

He preaches rereats and parish missions in Ireland, Great Britain and the USA, and is the spiritual director to the National Council of Youth 2000, Ireland.