Antonius is a masculine given name, as well as a surname. Antonius is a Danish, Dutch, Finnish, Latin, Norwegian, and Swedish name used in Greenland, Denmark, Norway, Sweden, Finland, part of the Republic of Karelia, Estonia, Belgium, Netherlands, Suriname, South Africa, Namibia, and Indonesia, while Antoníus is an Icelandic name used in Iceland. It is also the source of the English personal name Anthony, as well as a number of similar names in various European languages.

Antonius is the nomen of the gens Antonia, an important plebeian family of ancient Rome. Marcus Antonius claimed that the gens was descended from Anton, a son of Hercules. Women of the family were called Antonia. The Antonii produced a number of important generals and politicians, some of whom are listed below. For other persons with this name, see Antonia (gens).

• Marcus Antonius (83–30 BC), ally of Caesar, triumvir and afterwards enemy of Augustus. Probably the most famous of the Antonii, his life is depicted in William Shakespeare's play Antony and Cleopatra. He promulgated the leges Antoniae of 44 BC, abolishing the office of dictator, re-adjusting provincial commands, confirming Caesar's acta, and granting provocatio to those convicted de maiestate and de vi.