The death of his father in 1641 made him one of the wealthiest magnates in the entire Commonwealth. In 1646 he became a member of the senate of Poland, as he an important office that granted him this privilege: in April that year, he became the Field Hetman of Lithuania. Later, in November, he also received another prestigious title, that of a starost of Samogitia. In 1648 he was elected to the Lithuanian Tribunal. Later that year, the Commonwealth suffered two drastic events: death of king Władysław (succeeded by Jan Kazimierz Waza), and the beginning of the Chmielnicki Uprising. In February 1649 he commanded the Commonwealth forces in the victorious Battle of Mazyr, and in July, at Battle of Loyew. Fighting resumed in 1651, and Radziwiłł was once again victorious, commanding the Lithuanian forces at the Second Battle of Loyew in July, capture of Kiev on 4 August, and the Battle of Bila Tserkva in September.