Battle of al-Qādisiyyah
He was among the commanders at the Battle of al-Qādisiyyah. In 636, after the capture of Persian territory in Iraq by Muslim Arab forces and the departure of Khalid ibn al-Walid, al-Muthanna was put in charge of Muslim Arab occupied territories of Iraq. Al-Muthanna relied on his tribe, the Bakr along with other powerful Arab tribes including the Taghlib and the Tamim to maintain control over the territories.