Lentaigne, John Francis O'Neill (1803–86), physician, of Tallaght, Co. Dublin, was born 21 June 1803, eldest son among four children of Benjamin Lentaigne (qv) (1773–1813), a French physician who settled in Dublin after the French revolution, and his wife Marie Thérèse (d. 1820), daughter and heiress of John O'Neill (qv), a wealthy tradesman and a delegate to the Catholic Convention of 1792. He was educated at Clongowes Wood and studied medicine at the University of Dublin, where he graduated MA (1825) and MB (1828), becoming a licentiate of the RCSI (1830) and fellow of the RCPI (1844). He purchased Tallaght demesne in the 1830s, and renovated the house to accommodate his collection of antiquities and curiosities. Part of the demesne was leased to the Dominican order in 1842. A younger brother, Joseph Lentaigne (1805–84), was one of the first two Irish Jesuits to go to Australia in 1865, and began the Irish mission in Melbourne.
Lentaigne was a favourite of the Irish administration at Dublin Castle and served on many government bodies, as commissioner of loan funds (1841), inspector general of prisons (1854–77), inspector of reform and industrial schools (1870–86), and commissioner of national education (1861–86), as well as JP and high sheriff (1844) to Co. Monaghan. He unsuccessfully contested the Dublin county seat in the liberal interest in the general election of July 1852. Proper treatment and care of the insane was one of his great interests and he served on the board of governors of the Richmond asylum, Dublin (1875–86). He was president of the Royal Zoological Society of Ireland and the Statistical and Social Inquiry Society of Ireland (1877–8) and a member of the RIA (April 1853), and was made CB (1873) and KCB (1880). He was appointed to the Irish privy council in May 1886. He died 12 November 1886 at his home in Great Denmark St., Dublin.
He married (13 September 1841) Mary (1819–87), daughter of Francis Magan (1791–1841) of Emoe, Co. Westmeath; they had seven sons and four daughters. A grandson, Maj.-gen. Walter David Lentaigne (1899–1955), succeeded Orde Wingate in command of the Chindits in Burma (1944). John Lentaigne's son Sir John Vincent Lentaigne (1855–1915), surgeon, born 19 July 1855 in Dublin, was, like his father, educated in Clongowes Wood College, and later at Vannes in Brittany. He received his medical education at the Catholic University of Ireland, Dublin University (1880), and the RCSI (1879) before entering the Richmond Hospital as resident surgeon in 1882, moving later to the Mater Misericordiae Hospital in 1886.
He served for many years on the council of the RCSI and was elected fellow (1886), vice-president (1906), and president (1908–9). His surgical technique was characterised by its thoroughness and he was appointed surgeon general to the household of the lord lieutenant (1911). He was knighted in 1910 and died 30 March 1915.
He married (February 1882) Phyllis Mary, the only daughter of John Coffey; they had three sons and two daughters.