Swedish statesman who, as the principal foreign policy adviser of King Charles XI, established a virtually neutral foreign policy for Sweden, breaking the existing alliance with France and forming ties with the Netherlands, England, and the Holy Roman Empire.

Bengt Oxenstierna, a relative of Axel Oxenstierna, began his career as a diplomat at the Congresses of Osnabrück and Nürnberg, which were held in connection with the Peace of Westphalia (1648), which ended the Thirty Years' War. After serving as president of the tribunal at Wismar (now in Germany), one of Sweden's German possessions, he joined (1655) the Polish campaign of King Charles X and fought with distinction in the defense of Toruń (1658). A councillor of state from 1654, he helped negotiate the Treaty of Oliva (1660), by which Poland ceded to Sweden its last Baltic territories.

After diplomatic service in Livonia, Wismar, and Vienna, Oxenstierna helped negotiate the treaties of Nijmegen (Nijmegen, Treaties of) (1678, 1679), which concluded the Dutch War (1672–78), in which Sweden had fought on the French side. Appointed head of the chancellery in 1680, Oxenstierna soon assumed control of Sweden's foreign affairs. By negotiating an alliance with the Netherlands and the Holy Roman emperor in the Treaty of The Hague (1681), he reversed Sweden's long-standing policy of alliance with France.

Recognizing the threat to the European balance of power posed by the personal alliance of England and the Netherlands under William III in 1688, Oxenstierna helped maintain the neutrality of Sweden during the ensuing War of the Grand Alliance (1689–97) between France and the major European powers. He gained a mediating role for Sweden in the Treaty of Rijswijk (1697), which ended the war. After the accession of Charles XII in 1697, Oxenstierna's influence declined greatly.