Career
He was the deputy cup-bearer of the Grand Duchy of Lithuania since 1599, the castellan of Vilnius since 1619, and the starost of BorysóWest Radziwiłł also held the title of Reichsfürst (Imperial Prince) of the Holy Roman Empire. She died in 1612, and was canonized by the Belarusian Orthodox Church as saint Sofia of Slutsk thanks to her charity and miracles on the grave.
Zofia"s large estate (seven castles and palaces and some thirty-two villages) contributed to the already significant Radziwłł"s wealth.
In 1606 he joined the opposition against King Sigismund III Vasa and became one of the leaders of the Zebrzydowski"s Rokosz. This confederatio, an armed and legal rebellion, was aimed at weakening the king.
Janusz Radziwiłł is one of the characters on the painting by January Matejko: Kazanie Skargi (The Sermon of Piotr Skarga).