During the Kalmar Union, he was co-regent of Sweden, together with his brother Bengt Jönsson Oxenstierna (1390s–1450s) from January to June 1448.
[1][2] Oxenstierna was son of important nobles and landowners: his mother Märta Finvidsdotter (Frössviksätten) was the heiress of the noble Frössvik family, and his father Jöns Bengtsson Oxenstierna (died 1396–99) was the son and one of the heirs of Ingeborg Nilsdotter (from family that is called the earliest Sparre in later historiography and genealogy), heiress of Ängsö and Salsta.
Jöns Bengtsson inherited Frössvik (in Uppland) from his mother and Ängsö (in Västmanland) from his father.
His third wife Katarina Karlsdotter bore a number of children of whom half died without marriage and issue.
A portion of Oxenstierna's properties passed ultimately to others than his direct descendants, as inheritances through his daughters-in- and sons-in-law.