St Mary’s is the cathedral church of the Roman Catholic Diocese of Ossory. It is situated on James’s Street, Kilkenny, Ireland.
Saint Mary’s was designed by William Deane Butler (c.1794-1857). He was chosen by Bishop William Kinsella (1793-1845) who instigated the building of St. Mary’s in February 1842. Work began in April 1843 and finished in 1857. On Sunday 4 October 1857, St. Mary’s had its grand opening, which consisted of a two-and-three-quarter hour ceremony that began at 6.15am. The cost of the building is estimated to have been £25,000.
St. Mary’s is made from cut-limestone which was sourced locally. The cathedral has a cruciform plan and its style is described as ‘Early English Gothic’.[ The design is believed to have been based on Gloucester Cathedral in Gloucester, England. It is situated on the highest point in Kilkenny City and is a significant local landmark.
The cathedral is variously referred to as "St Mary’s", "the church of St Kieran" and "the Cathedral of the Assumption".
St. Mary’s has a noted sculpture of the Madonna by Giovanni Maria Benzoni (1809-1873).