Parishioners have lobbied Aberystwyth Town Council to oppose the demolition of Our Lady of the Angels and St Winefride's Church and have written to the Archbishop of Westminster, Vincent Nichols.
But Bishop Tom Burns has told The Tablet that the building, which is still in use, is in such a state of disrepair that it is a danger to churchgoers and that the estimated cost of repair work would leave the parish with a debt in excess of £1m.
The bishop said that the sale of the existing site would completely finance the construction of a new church, presbytery and hall on a different site in a neighbouring town.