Lieutenant-General Sir Thomas McMahon, 2nd Baronet (1779–1860) was a British Army officer.

He had at least one sister, who married a Mr O'Halloran: her daughter, whose first name is uncertain, was the first wife of the writer and politician Richard Lalor Sheil.

While Thomas and William were both gifted men, their early careers were hampered by their relatively humble social origins, and there is little doubt that their half-brother's political influence greatly assisted them in their rise to prominence.

John was the first of the McMahon Baronets of Ashley Manor: on his death in 1817, the title passed to Thomas by special remainder.

[1] He went on to be Lieutenant-Governor of Portsmouth and General Officer Commanding South-West District in 1834[2] and became Commander-in-chief of the Bombay Army on 14 February 1840 retiring from that post on 8 April 1847.