Architect. Born at St. Martin's (Perth and Kinross), the son of Alexander Mackenzie, a builder and architect. Three of Mackenzie's brothers were also architects; William in Perth, David in Dundee and James in Liverpool, and it was with his eldest brother William MacDonald Mackenzie (1797 - 1856) that he trained. He is also known to have worked with David in the early 1830s. In 1835, he moved to Aberdeen to work with John Smith (1781 - 1852) and then with his great rival Archibald Simpson (1790 - 1847). Mackenzie moved to Elgin (Moray) in 1839, at first working with William Robertson, but within two years he had set up his own practice there. He was commissioned to design Elgin Museum in 1842, going on to build Forres Market Cross (1844). In the same year, he formed a partnership with James Matthews (1819-98), who had become a friend when Mackenzie was working with Archibald Simpson. Mackenzie did much of the design work in Elgin while Matthews managed their office in Aberdeen. Together they were responsible for Drummuir Castle (1845), Poorhouses in Aberdeen and Ellon (1847 and 1849 respectively), Ballindalloch Castle (1847), St. John's Episcopal Church (1850), Aldourie Castle (1853) and Dall House (1854), together with various churches, schools and banks and work on Cawdor Castle (1854).
Despite his early death from 'brain fever', said to have been brought on by an accident, Mackenzie had gained a reputation as an accomplished architect of the Classical and Italianate styles. He lies buried in the graveyard surrounding Elgin Cathedral, beneath a monument designed by Matthews.
Thomas's son was A. Marshall Mackenzie (1848 - 1933) who became a noted architect in Aberdeen.
