McCarthy was born in Cork, and was educated at a school there. He began his career as a journalist, aged 18, in Cork. From 1853 to 1859 he was in Liverpool, on the staff of the Northern Daily Times, during which period he married (in March 1855) Charlotte Ailman.In 1860 he moved to London, as parliamentary reporter to The Morning Star, of which he became editor in 1864.He gave up his post in 1868, and, after a lecturing tour in the United States, joined the staff of the Daily News as leader-writer in 1870. In this capacity he became one of the most useful and respected upholders of the liberal politics of the time. He lectured again in America in 1870-1871, and again in 1886-1887.McCarthy's real bent was towards literature. His earliest publications were novels, some of which, such as A Fair Saxon (1873), Dear Lady Disdain (1875), Miss Misanthrope (1878), Donna Quixote (1879), attained considerable popularity. His most important work is his History of Our Own Times (vols. i.iv., 1879–1880; vol. v., 1897),which treats of the period between Queen Victoria's accession and her Diamond Jubilee. Easily and delightfully written, and on the whole eminently sane and moderate, these volumes form a brilliant piece of narrative from a Liberal standpoint. He also began a History of the Four Georges (1884 1901), of which the latter half was written by his son, Justin Huntly McCarthy.He also collaborated on three novels with Rosa Campbell Praed: The Right Honourable (1886), The Rebel Rose (issued anonymously in 1888 but appeared in their joint names in two later editions under the title, The Rival Princess), and The Ladies' Gallery (1888). They also collaborated on The Grey River, a book on the Thames, which was illustrated with etchings by Mortimer Menpes. McCarthy also wrote 'The Story of Gladstone' (1904) a somewhat uncritical biography of William Ewart Gladstone that betrays the authors sympathies with Irish nationalism. Particularly amusing herein is McCarthy's characterisation of Palmerston.