Chlothar IV (or Chlotar, Clothar, Clotaire, Chlotochar or Hlothar, giving rise to the name Lothair; died c. 719), king of Austrasia (717–18), was installed by the mayor of the palace, Charles Martel, as an ally during the civil war 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 Chlothar 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. Charles now recognized Chilperic as king of all the Franks, and in exchange Chilperic surrendered his political power to Charles, who gained a monopoly on power and royal offices.

Chlothar is thought to have died in 718. When Chilperic was raised on the shield in 719, Charles may have been willing to recognize him as king as a result of Chlothar's death. It is possible, however, that Chlothar survived until 719, 720 or even 721. It is also possible that Chlothar was a son (or grandson) of Childebert III or not a Merovingian at all, but merely a puppet or place-man who served Charles Martel's political purposes at the time.