Following graduation he served as a CUSO (Canadian University Services Overseas) volunteer in Ghana teaching French in a secondary school.
In 1977 he entered Le Grand Séminaire de Québec, and was ordained to the priesthood for the Diocese of Prince Albert on June 19, 1983, by Bishop Blaise Morand.
For the next seventeen years (1983–2000) he served in a number of parishes in the diocese, as well as co-ordinator of the Diocesan Liturgical Commission, Director of Vocations and Consultor.
LeGatt's Episcopal motto is Ut Unum Sint (Latin: That They May Be One) and is taken from Chapter 17, Verse 22 of The Gospel According to John.
He is Chairman of the Episcopal Commission for Liturgy and the Sacraments – English Sector for the Canadian Conference of Catholic Bishops and a Fourth Degree member of the Knights of Columbus.