 Ordained in 1846 in 1847 he moved to India, where he served as a School principal, and Army Chaplin and priest in the Madras Vicarate.Colgan was honoured by being named a Fellow of Madras University.Colgan was appointed Bishop of Madras in 1882 succeeding Bishop Stephen Fennelly and became the first Archbishop of Madras in 1886, 

Colgan served as archbishop until he died on 13 February 1911.