Justin M'Carthy (22 November 1830 - 1912) was an Irish politician, historian and novelist.

He was born in Cork, and was educated at a school in that town. He began his career as a journalist, at the age of eighteen, 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) Miss Charlotte Ailman. In 1860 he removed 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.

He represented County Longford in Parliament as a Liberal and Home Ruler from 1879 to 1885; North Longford , 1885-1886; Londonderry, 1886-1892; and North Longford from 1892 to 1900. He was chairman of the Anti-Parnellite wing of the Nationalist Party after the fall of Charles Stewart Parnell for a year in 1891-1892; but his nationalism was of a temperate and orderly kind, and though his personal distinction singled him out for the chairmanship during the party dissensions of this period, he was in no active sense the political leader.

His 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 M'Carthy (b. 1860), himself the author of various clever novels, plays, poetical pieces and short histories. Justin MCarthy, amongst other works, wrote biographies of Sir Robert Peel (1891), Pope Leo XIII (1896) and W. E. Gladstone (1898); Modern England (1898); The Reign of Queen Anne (1902) and Reminiscences (2 vols., 1899).