Lothian was born on 25 December 1915 in the Melbourne, suburb of Mont Albert. After completing school, he studied at Burnley Horticultural College. He worked in botanical gardens in Melbourne and at the Christchurch Botanic Gardens in New Zealand, then started study at the Royal Botanic Gardens, Kew in 1938. Lothian was an exchange student at the Munich Botanic Garden when the Second World War broke out. After returning to the United Kingdom to complete studies at Kew Gardens, he joined the Australian Army and managed farms in New Guinea.
After the war, Lothian studied and lectured at the Lincoln Agricultural College in New Zealand. In 1948 he was appointed director of the Adelaide Botanic Garden, a position he held until 1980. While there, he was a prominent member of the Royal Society and chairman of its offshoot, the Field Naturalists Society for several years. In 1961 he was awarded an OBE for services to horticulture, and in 1975 the Veitch Medal of the Royal Horticultural Society. He died on 24 September 2004 in Townsville, Queensland.
- "Harvard University Herbaria - Index of Botanists - Lothian, Thomas Robert Noel". Harvard University Herbaria. Harvard University. Retrieved 12 July 2014.
- "Thomas Robert Noel Lothian - 25 December 1915–24 September 2004" (PDF). New Zealand Garden Journal. Royal New Zealand Institute of Horticulture. 2006. Retrieved 12 July 2014.
- "Thomas Robert Noel Lothian, O.B.E., N.D.H.(N.Z.) , L.F.R.A.I.P.R., J.P., President 1987/88" (PDF). The Kew Trust. Royal Botanic Gardens, Kew. 1988. Retrieved 12 July 2014.
- "State Library of South Australia - Thomas Robert Noel Lothian, O.B.E." (PDF). State Library of South Australia. 5 September 2011. Retrieved 12 July 2014.
- IPNI. Lothian.