Harris received a government pension in 1748, which enabled him to work on histories and religious writings.
In the 1730s, along with others of his time, Harris supported a scheme to compile and publish histories of all Irish counties.
He also started to revise and republish the historical and topographical writings of Sir James Ware, translating them from Latin to English.
The first to be published was Historiographorum Aliorumque Scriptorum Hiberniae Commentarium: or, a history of the Irish writers (Dublin, 1736).
To increase the attractiveness of these books he commissioned from Jonas Blaymire drawings of buildings and their contents.