Emergency services attended the scene of a fire at the Cork Unitarian Church Princes St shortly after 8am on Monday, with a spokesperson from Cork City Fire Brigade saying the fire caused "very significant damage".
A section of Oliver Plunkett St was closed off to deal with the fire.
While the historic building was saved, and the roof remains intact, the interior suffered serious damage.
"The interior damage is extensive. The historic building is saved but the usability of the interior for church services and all other activities has been severely compromised," said a statement from the church.
Cork City Fire Brigade said the fire was not being treated as suspicious and no injuries have been reported.
Minister Reverend Mike O'Sullivan was on site shortly after the fire broke out.
The statement added that Rev O'Sullivan and the church committee "were devastated and are assessing how to proceed going forward".
Rev O'Sullivan told the Irish Examiner: "The work of the church is larger than the building. We will inform the public at a later date where the Church will meet to continue its work."
He also offered his "deepest thanks and appreciation "to the Cork City Fire Brigade and gardaÃ.