On his father's side, he was a member of the aristocracy as a descendent of Danish Pricy Councillor Niels Eriksson to Aagaard and Restrup in Jutland.

The National Archives of Sweden notes that his first audience with Elizabeth I took place on 2 April 1561 and the Queen declined the marriage proposal.

[9] Gyllenstierna wrote: "Her Majesty [Queen Elizabeth I] reacted noticeably, though this manoeuvre did not bring about any decisive change either"By the summer of 1561, Eric XIV had contemplated whether or not he should assassinate his love-rival, Leicester.

In response to Emperor Maximilian II’s protest against Swedish trade policy in Estonia, including the blockade of Narva, Gyllenstierna was also tasked with the delivery of Eric XIV correspondence and the negotiations between the states.

The envoy of Eric XIV did not achieve any concrete results, and the Holy Roman Empire retained its opposing stance to the Baltic issue.

Near the Swedish skerries, they encountered Danish warships that had seized the salt ships of merchants from Lödöse, forcing them to head toward the Norwegian coast.

In the letter, he emphasized the need to lift the Danish blockade of Älvsborg so that: "the Western Sea becomes free and unobstructed for all supplies to the Swedish realm.

The following summer, Gyllenstierna stayed in Rostock, where he had to deliver Erik XIV's apology for the absence of the Swedish envoys from the peace congress, related to Northern Seven Years' War, and scheduled to be held in the same city.

Subsequently, Gyllenstierna began negotiations with John Frederick II of Saxony-Weimar for an alliance with Sweden against Denmark and Elector Augustus of Saxony.

He retained his position as Lord High Chancellor of Sweden, was appointed Lawman of the Tiohärad district in 1569, and was made a baron that same year.

The position likely proved too burdensome for him due to his poor health, for when the king tasked him on January 4, 1577, to continue in the role, he was provided with some younger noblemen to assist him.

At the parliamentary session of 1587 in Vadstena, he was among those who brokered the reconciliation between the brothers.When the decision was made for Sigismund to travel to Poland, it is reported "though without solid evidence"that Gyllenstierna opposed the journey.

As much as he could, he withdrew from politics, sometimes citing his ill health, other times declaring that "the Polish affairs were far beyond his understanding," but he preferred to align himself with the stronger party.

As the Lord High Steward of Sweden, he opened the Uppsala Synod in 1593 with a speech urging those present to uphold the Augsburg Confession.

He also signed the council's letter of apology for not being able to attend the Riksdag in Arboga in 1597 but quickly excused himself with the peculiar explanation that he had not had time to read it thoroughly.

When Charles later sought his opinion on the Arboga Riksdag, he responded evasively but assured the Duke of his humble service in anything that could benefit the fatherland.