Carlos O'Neill (Lisbon, Santa Catarina, 9 June 1760 – 24 June 1835), was the titular head of a branch of the Clanaboy O'Neill dynasty, whose family has been in Portugal since the 18th century.
He was the first child and only son of the previous head João O'Neill and wife Valentina Maria Josefa Ferreira.
Carlos O'Neill was a trader, a Professed Knight of the Order of Christ, Lord of many Majorats and of the Farms Quinta dos Bonecos and Quinta da Saboaria, at the term of Setúbal, etc. He also inherited from his father in law the Casa Comercial Torlades, of which he became the Main Manager, and the Farm Quinta das Machadas, in the Parish of São Julião, term of Setúbal, of which he became Lord by purchase. On 25 May 1825 the Farm was visited by King John VI of Portugal, accompanied by the Infanta Isabel Maria of Portugal and the Infanta Maria da Assunção of Portugal, and by the Court, being received and hosted by its Proprietor, the mentioned Carlos O'Neill, for whom the mentioned farm had passed on to, by marriage, by which the Crest of the O'Neill Family was placed over the door of the western front, etc.
He married in Lisbon, Sacramento, on 17 September 1784 to Ana João Torlade, daughter of Jacob Frederico Torlade and wife Maria Inácia Gonçalves, and had issue, nine children: