A native of Aberystwyth, John attended Ysgol Penglais before studying law at the University of Wales, Cardiff.

[5] Until his election as Bishop of Bangor, all his ministry was in the Diocese of St David's.

From 1999 he was vicar of Henfynyw with Aberaeron and Llanddewi Aberarth, to which was added Llanbadarn Trefeglwys in 2005.

[7] On 6 December 2021, John was elected to serve as Archbishop of Wales (remaining Bishop of Bangor) by an Electoral College of the Church in Wales meeting at Holy Trinity Church, Llandrindod Wells; his election was confirmed (and therefore he legally took up the archiepiscopal see) immediately.

[9][10] He was honoured as a member of Gorsedd Cymru in 2023[11] as were two previous archbishops of Wales, Barry Morgan and Rowan Williams.