[citation needed] In 1891, Gilmartin served as Dean of Formation and Vice-President of St Patrick's College, Maynooth.

[citation needed] He was appointed the Bishop of the Diocese of Clonfert by the Holy See on 3 July 1909 and was consecrated on 13 February 1910 by the Most Reverend John Healy, Archbishop of Tuam.

[5] Gilmartin counseled his priests that whatever their personal political beliefs, they should not take an aggressive part on behalf of either side.

[6] Gilmartin was involved in the controversy over the appointment of Letitia Dunbar (a member of the Church of Ireland and graduate of Trinity College, Dublin) to the County Mayo librarianship in 1931.

[2][4] Gilmartin wrote the Memoir of Primate Joseph Dixon in Healy's Centenary History of Maynooth in 1895.