Swanachild (also Swanahild or Serenahilt) was the second wife of Charles Martel, who brought her back from his first campaign in Bavaria in 725, along with her uncle Grimoald's wife, Biltrude. Swanachild belonged to the clan of the Agilolfings though her parentage is not quite clear. Her parents could be:
- Tassilo II, duke of Bavaria, and his wife Imma
- Theodbert, duke of Bavaria and his wife Regintrud
With Charles Martel she had one child, Grifo. After the death of Charles, she supported her son's failed attempt to gain a portion of his inheritance. This she did with the support of her uncle Odilo of Bavaria. Afterwards she was relegated to the position of abbess of Chelles. Although later Carolingian historians cast her as a concubine, she was during her time the rightful wife of Charles. The Reichenau Codex listed her as Suanahil regina, "Queen Swanachild."