Sigismund II Augustus was the only son of Italian-born Bona Sforza and Sigismund the Old. From the beginning he was groomed and extensively educated as a successor. In 1529 he was crowned vivente rege while his father was still alive. Sigismund Augustus continued a tolerance policy towards minorities and maintained peaceful relations with neighbouring countries, with the exception of the Northern Seven Years' War which aimed to secure Baltic trade. Under his patronage, culture flourished in Poland; he was a collector of tapestries from the Low Countries and collected military memorabilia as well as swords, armours and jewellery. Sigismund Augustus' rule is widely considered as the apex of the Polish Golden Age; he established the first regular Polish navy and the first regular postal service in Poland, known today as Poczta Polska. In 1569 he oversaw the signing of the Union of Lublin between Poland and the Grand Duchy of Lithuania, which formed the Polish–Lithuanian Commonwealth and introduced an elective monarchy.

Sigismund Augustus was the last male member of the Jagiellons. Following the death of his sister Anna in 1596 the Jagiellonian dynasty came to an end.