Sisenand was the governor of Septimania when there was an uprising of the nobles against the confiscations of lands and the cut of privileges to them and the clergy that were propounded by Suintila. Sisenand defended the nobles and the clergy and overthrew Suintila with the aid of Dagobert I, King of the Franks, to whom Gothic nobles offered a plate of pure gold in return, weighing 500 pounds. It is allegedly a gift that Aetius, a Roman general, gave to Thorismund, the king of the Visigoths in 451. After successfully overthrowing Suintila and capturing Zaragoza, on 26 March 631, he proclaimed himself king of the Visigothic kingdom. The victory of Sisenando was the victory of the privileges of the nobility over the common people, while the greatest beneficiary was the clergy, who took advantage of the wearers of the contenders to reinforce their influence.
During his rise to kingship, he had Suintila, the previous king, declared a tyrant for his many crimes, iniquity, and accumulation of wealth at the expense of the poor while also removing all taxes on the clergy
In order to obtain ecclesiastical conformity, on 8 December 633, Sisenand convoked the IV Council of Toledo, which drew up civil and ecclesiastical laws within the Visigothic kingdom, it was also approved that anyone who rose against the king should be sentenced to death, excommunicated and condemned to perpetual perdition. Similar penalties were approved for those who wished to dispense with such law of choice. However, the council did not concede any hereditary right to the king; the next king would be elected by the bishops and magnates from one of their own.