Rees is best known for the editorial work he did for the Welsh Manuscripts Society. The society's edition of the Liber Landavensis was transferred on the death of his nephew Rice Rees to him in 1839, and the book appeared in 1840. In 1853 Rees also edited for the society Lives of the Cambro-British Saints (text and English translation). Both of these works were subject to later criticism.[2]
In 1803 Rees published A Short and Practical Account of the Principal Doctrines of Christianity, in 1809 an essay on Clerical Elocution, and in 1811 a tract on pastoral work.[2]