In July 1658, he commanded the garrison of Thorn, now Toruń when it was besieged by an Imperial-Polish force, surrendering in December; he later helped negotiate the peace of Oliva that ended the war.

[3] Oxenstierna generally supported closer relations between Sweden and the Holy Roman Empire, placing him in opposition to the pro-French faction headed by Magnus de la Gardie.

While there, he presented a 'Memorial' or paper to Emperor Leopold titled The case of the persecuted and oppressed Protestants in some parts of Germany and Hungary, which was later published in London.

[6] When his chief minister Johan Göransson Gyllenstierna died in 1680, Charles appointed Oxenstierna President of the Court of Chancery, a position that traditionally controlled foreign policy.

[7] Oxenstierna moved Sweden away from its traditional pro-French alliance, instead following a policy of friendship with England, the Dutch Republic and the Holy Roman Empire.

[8] As President of the Court of Chancery, he was also de facto Minister of Culture, approving all publications; author and military engineer Erik Dahlbergh (1625-1703) dedicated several books to him.