Ideas for the cathedral started when it became clear that Catholics in Ireland would be emancipated and be able to practise their religion with the same rights as Protestants thus the church was donated what was in 1823 a marsh. This was was then drained and construction started allowing the church to open just before the Emancipation Act.
Originally built to a cost of £8,000 in 1829, the cathedral was gradually extended throughout the 19th century, a rare occurence for a Victorian cathedral.
The tower and transept were added in 1888. It's due to this that the actual date etched in stone on the cathedral claims it was completed in 1888 although there was further work on the nave in 1904.
The original parts of the cathedral were built by local craftsmen using local granite, although rumour has it the stonemasons were mixed up and Thomas Duff had those who had been hired for Dundalk Cathedral work on it by accident. In turn, the workmen hired for Newry Cathedral ended up working on Dundalk.
Mindful of the more extravagant detailing to later parts, not to mention the desire for an accurate Catholic expression of sculpture, to complete the tower skilled stonemasons were brought in from Italy.