He moved from Edinburgh to Sheffield, and from there to Bolton, where he developed a considerable trade in the textile fabrics of all kinds worn by clergymen and otherwise used in the services of the church.
In July 1840 a communication signed with his initials appeared in the Gentleman's Magazine which contained a sketch of the story of James Annesley, with indications of its resemblance to that of Henry Bertram in Guy Mannering.
French expanded this communication in a pamphlet "printed for presentation" in 1855 and entitled Parallel Passages from Two Tales, elucidating the Origin of the Plot of "Guy Mannering".
Beginning on 26 April 1856, he contributed a series of letters to consecutive numbers of the Bolton Chronicle, which he collected and again "printed for presentation" in the same year as An Enquiry into the Origin and Authorship of some of the Waverley Novels.
Here French developed, with new facts and illustrations, the old theory, revived by W. J. Fitzpatrick in 1856, that Scott's brother Thomas and his wife were the virtual authors of the earlier Waverley novels.