 Marello underwent the clerical investiture on 9 January 1864, and received both the tonsure and all minor orders from Bishop Savio on 21 December 1867.He was made a subdeacon on 28 March 1868, and was elevated to the diaconate on 6 June 1868.Marello was ordained to the priesthood on 19 September 1868 with Savio again officiating.