Cullen served as rector to St. Mary's Knockbeg College from 1895 until 1909, when he moved to Newbridge, prior to being appointed parish priest of Tinyland and then Bagenalstown before being elected a bishop.
[citation needed] He was a keen supporter of Gaelic Games and regularly attended GAA matches in Kildare and Carlow.
[citation needed] In 1927 he was appointed Bishop of Kildare and Leighlin, succeeding Dr. Patrick Foley and served until his death.
[4] Cullen encouraged and facilitated the establishment of St Patrick's Missionary Society at Kiltegan.
Following his death Carlow GAA Stadium, which had just been completed, was named Dr. Cullen Park in his honour.