Walsh was born in Wexford, Ireland, and graduated in medicine from University College Dublin in 1944. During his years in Dublin he took singing lessons from Adelio Viani at the Royal Irish Academy of Music. In 1972, he completed a Ph.D. at Trinity College, Dublin, the thesis becoming the basis for his 1973 book on Opera in Dublin.
He became chairman and artistic director of the Wexford Festival in 1951 and established its international recognition over 15 years while still working as an anaesthetist at Wexford County Hospital. Known locally as "Doctor Tom" he "inspired great affection, admiration, and, given his great learning, even a measure of awe".
Walsh wrote several books relating to opera, covering 18th century Dublin, opera in Monte Carlo and the Théâtre Lyrique in Paris:
- Opera in Old Dublin, 1819–1838 (Wexford: The Free Press, 1952)
- Opera in Dublin, 1705-1797: the Social Scene (Dublin: Allen Figgis, 1973)
- Monte Carlo Opera, 1879–1909 (Dublin: Gill and Macmillan, 1975); ISBN 978-0-7171-0725-4
- Second Empire Opera: The Théâtre Lyrique Paris 1851–1870 (London: John Calder & New York: Riverrun Press, 1981); ISBN 0-7145-3659-8
- Opera in Dublin, 1798–1820: Frederick Jones and the Crow Street Theatre (Oxford: Oxford University Press, 1993); ISBN 0-19-816397-5
- Boydell, B.: "Walsh, T(homas) J(oseph)", in: New Grove Dictionary of Opera (London and New York: Macmillan, 1997).
- Barra Boydell: "Walsh, Thomas J.", in: The Encyclopaedia of Music in Ireland, ed. Harry White & Barra Boydell (Dublin: UCD Press, 2013), p. 1042–3.
- Wexford Festival Opera. 62nd Festival 23 October - 3 November 2013, p. 5.
- Karina Daly: Tom Walsh's Opera. A History of the Wexford Festival, 1951–2004 (Dublin: Four Courts Press, 2004); ISBN 1-85182-878-8.
- Obituary in Opera magazine, January 1989, p. 38.