Harris agreed on 12 August 1695 to build a new organ for St Patrick's Cathedral which was completed in 1697. Cuvillie is thought to have been involved in building this instrument. In May 1697, one week after finishing the St Patrick's instrument, he was engaged to build a new organ for Christ Church Cathedral. Part of this instrument was the organ that Harris had used for the famous 'battle of the organs' with Bernard Schmidt ('Father Smith') in London. Grindle suggests that 'it is probable that this organ was not set up at Christ Church by Harris's men, but that on delivery from London it was assembled by the Dublin builder John Baptiste Cuvillie'. It is possible that Harris may not have visited Dublin in person.