He was apprenticed as a "writer" (the Scots term for a lawyer) by Mr James Stark the Procurator for Fife, based in Cupar.
[1] He became familiar with the writings of the Richard Brothers who had begun a millennium cult in Britain based on the belief that a second Israel would be created and a new Messiah appear.
Brothers led him to change the spelling of his name, by telling him his ancestors had some 'fine leys' of land granted them for deeds of valour.
[3] He printed a variety of pamphlets, reiterating Brothers's views, and developing his own peculiar notions of astronomy, for which he claimed a divine origin.
Finlayson printed: Also nine large sheets of the ground plan of the New Jerusalem (with its 56 squares, 320 streets, 4 temples, 20 colleges, 47 private palaces, 16 markets, &c.); and twelve sheets of views of its public buildings; all these executed by Finlayson for Brothers (the original copper-plates were in the hands of Beauford, whose price for a set of the prints was 38l.)