Buchanan’s father, the only son of an eminent Glasgow lawyer, was in business in the city as a hat maker, and was described the year before his death as ‘a very independent man’ who had recently bought a vote for Dunbartonshire. Of his half-brothers from his father’s second and third marriages, James (1766-1855) was founder of the family of Gray Buchanan of Eastfield, and William (1777-1864) achieved some success in London as an art critic and picture dealer.
He was a fairly regular attender, who gave general but silent support to government. Although he voted for repeal of the additional malt duty, 21 Mar., he rallied to ministers when they threatened resignation on the issue, 3 Apr. 1821. He divided against the disfranchisement of ordnance officials, 12 Apr., parliamentary reform, 9, 10 May, and the forgery punishment mitigation bill, 23 May. He voted against the omission of arrears from the duke of Clarence’s grant, 18 June 1821. He divided against more extensive tax reductions, 11, 21 Feb., and abolition of one of the joint-postmasterships, 13 Mar. 1822. He presented petitions for relaxation of the distillery laws, 29 Apr., 21 May.
Buchanan retired at the dissolution in 1826. He disposed of Balloch in 1830 and bought a property at Boturich.
