The Basilica Museum - Mullock Library is the main repository for antiquities and vestments of the Roman Catholic Archdiocese of St. John's.

Some of the Antiquities and Vestments:

• Sacred vessels from the Basilica Sacristy and various parishes
• Pictures of the bishops and archbishops of St. John's, from the first pastor and Perfect Apostolic James Louis O'Donel in 1784 through to the present Archbishop
• A sculpture, The Infant Jesus by renowned Irish sculptor John Edward Carew
• Archbishop Roche's ermine Cappa Magna, or great cape and other ceremonial vestments
• A massive lare 19th century reproduction oak table with eighteen chairs, in the "Jacobethan" style
• A  large collection of books in many languages; the oldest ones dating from the 1500s