Alternate renditions of his name include Lithuanian: Mikalojus Radvila Juodasis, Belarusian: Мікалай Радзівіл Чорны, and Latin: Nicolaus Radvil.

[1][3] Mikołaj was able to gain much political influence thanks to the romance and then the marriage between his cousin Barbara Radziwiłł and the King of Poland and Grand Duke of Lithuania Sigismund II Augustus.

The growing influence of the Radziwiłł family was further bolstered when, during a diplomatic mission to Charles V and Ferdinand I, he and his cousin Mikołaj the Red received a hereditary title of Prince (Reichsfürst (SRI)).

[4] He formed an alliance with his cousin Mikołaj "the Red" Radziwiłł against other notable Lithuanian families in the rivalry for the dominant status in the Great Duchy of Lithuania.

[4] Mikołaj contributed to the ongoing Polonisation of the Grand Duchy, influencing other Lithuanian nobles to follow him in adopting Polish culture – its fashion, customs and language.