Ashton Oxenden was born at Broome Park, Kent, England, the son of a country squire. After graduating from University College, Oxford he was made curate of the rural parish of Barham. After six years, ill-health forced him to suspend his clerical duties, returning in 1848, to become briefly curate of Silsoe then rector of Pluckley, another rural parish. Over the next 21 years he published more than 100 pamphlets and 25 books, selling several hundred thousand copies.
His election as Bishop of Montreal and Metropolitan was a compromise largely based on his reputation as a writer. After two sessions and 14 ballots, the Synod of 1868–69 had been unable to agree on a bishop. The penultimate vote had been between Benjamin Croyn, Bishop of Huron, and Rev Dr Meyrick of England, with the majority of lay votes for Cronyn and the majority of clerical votes for Meyrick. In the final vote 2 new names were submitted with Rev Ashton Oxenden winning over Rev Dr Monsell.
The new bishop arrived at Montreal in late summer 1869 to a diocese of 59 parishes, only 8 of which self-supporting. In 1871 he established a "sustentation fund" but this only moderately improved the financial state of the diocese. Bishop Oxenden determined there were not enough clergy so he both encouraged the immigration of English clergymen to Montreal and in September 1873 opened the Montreal Diocesan Theological College to train Canadian clergy.
In 1878 Dr Oxenden went to England to attend the Lamberth Conference and while there he unexpectedly resigned his bishoric. Ashton Oxenden died at Biarritz, France 23 February 1892 at the age of 84.