The Monteath's were prominent Glasgow manufacturers & merchants. A James Monteath, son of Walter Monteath of Kepp & Jean Douglas daughter of James Douglas of Mains & Rebecca Wallace, was a partner in the firm of Hamilton, Monteath & Co, wine merchants & stamp distributers. He inherited the fortune of his elder brother Major Archibald Monteath who, rumour had it, had looted a treasure elephant in India. He also succeeded to the estate of Rosehall and took the name Douglas.
Henry Monteath of Carstairs, son of James Monteath, was a manufacturer & exporter of bandanas, he was twice Lord Provost of Glasgow & MP for Linlithgow, married twice, to Christina Cameron & Sarah Fullerton.
The family were also members of a Glasgow club named "The Board of the Green Cloth", but whether these are your Monteath the writer (lawyer) is something for you to find out.
Bests,
Skoosh.