Oxenstierna was born on 16 June 1583, at Fånö in Uppland, the son of Gustaf Gabrielsson Oxenstierna (1551–1597) and Barbro Axelsdotter Bielke (1556–1624), as the oldest of nine siblings. His parents belonged to the ancient and influential high noble families of Oxenstierna and Bielke, both of which had held high offices in the state and the church for generations. After the death of her husband Gustaf, Axel's mother Barbro decided to let Axel and his brothers Christer and Gustaf finish their studies abroad. Thus, the brothers received their education at the universities of Rostock, Wittenberg and Jena. On returning home in 1603 he took up an appointment as valet de chambre (kammarjunkare) to King Charles IX of Sweden.
