St. Mary's Church is a Grade B-1 listed Catholic church located in Chapel Lane/Smithfield area of Belfast, Northern Ireland. A church was opened on this site in May 1784 and thus it is the mother church for the city of Belfast. At the time, it was the only Catholic church in the then town of Belfast after the relaxation of some of the Penal Laws. The church grounds contain an undistinguished grotto dedicated to Our Lady of Lourdes. Until 2022 St. Mary's was a mensal parish of the Diocese of Down and Connor.

The Diocese of Down and Connor, is a Latin Church ecclesiastical territory or diocese of the Catholic Church in Northern Ireland. It is one of eight suffragan dioceses in the ecclesiastical province of the metropolitan Archdiocese of Armagh. Bishop Alan McGuckian is Bishop.