Justin Huntly McCarthy (1859 – 20 March 1936) was an Irish author and nationalist politician. He was a Member of Parliament (MP) from 1884 to 1892, taking his seat in the House of Commons of the United Kingdom.
He was the son of Justin McCarthy (1830–1912). Since both father and son were authors, historians, and Members of Parliament, they are sometimes confused in lists and compilations.
McCarthy was first elected to Parliament at a by-election on 12 June 1884, when he was returned unopposed as the Home Rule League member for Athlone, following the death of the Liberal MP Sir John James Ennis.
Athlone lost its status as a parliamentary borough under the Redistribution of Seats Act 1885, and at the 1885 general election McCarthy stood instead in the borough of Newry in County Down, where he was returned unopposed for the Irish Parliamentary Party. He was re-elected in 1886, with a comfortable majority over the Liberal Unionist Reginald Saunders, but did contest the 1892 election.