From 1988 until 1995 he received his priestly formation at the Pontifical Scots College and the Pontifical Gregorian University in Rome, Italy, graduating with Baccalaureate in Sacred Theology (STB) and Licentiate in Philosophy (PhL) degrees.

In 2000 he was appointed chaplain to the Catholic students and staff of the University of Glasgow, a post he held until his episcopal ordination.

[7][8] Keenan was consecrated bishop in St Mirin's Cathedral, Paisley on 19 March 2014, the Feast of Saint Joseph by Archbishop Philip Tartaglia of Glasgow.

[4] Keenan has taken as his episcopal motto the words Suscepit servum recordatus misericordiae (He protects his servant remembering his mercy) inspired by the Magnificat.

[9] Having served as vice-president,[10] he was elected president of the Catholic Bishops Conference of Scotland in 2024.