Chlothar IV (or Chlotar, Clothar, Clotaire, Chlotochar, or Hlothar, giving rise to Lothair; died ca. 719), king of Austrasia (717–18), was installed by the mayor of the palace, Charles Martel, as an ally during the civil war that was then raging.

In 717, Charles, returning to Neustria with an army to assault King Chilperic II and his mayor Ragenfrid, confirmed his supremacy with a victory at Vincy, near Cambrai. He chased the fleeing king and mayor to Paris before turning back to remove his other opponent Plectrude from Cologne. On succeeding there, he proclaimed one Clotaire king of Austrasia in opposition to Chilperic, who supported Ragenfrid, not Charles, for the mayoralty. In 718, Chilperic was again defeated, at Soissons, by Charles. The king fled with his ally Odo the Great, duke of Aquitaine, to the duke's territory. Soon Odo gave up on Chilperic and sued for peace. In exchange for recognising his kingship over all the Franks, Chilperic surrendered his kingdom to the mayoralty of Charles, who gained a monopoly on power and royal offices.