Kaas belonged to a noble family. His parents were Niels, who died seven months before he was born, and Anne Bjørn, who died when he was five. As a result, Kaas was raised by his uncle Mogens Kaas, the dean of the district of Jelling, and later cantor of Ribe Chapel. He was educated at the Viborg school, where he studied for nine years, concentrating on theology and classical studies. In 1549, Kaas moved to Copenhagen, where he was taken in by theologian Niels Hemmingsen under the direction of his brother Bjørn. Under Hemmingsen, he completed his theological, Latin, and historical training. In 1554, Kaas began studying under Philipp Melanchthon in Wittenberg. He also studied in Frankfurt and Leuven, and saw the Battle of St. Quentin in 1557. He returned to Copenhagen in 1557, entering the Danish Chancery three years later. His knowledge of history and Latin became invaluable in negotiations with other countries. During the Northern Seven Years' War, Kaas remained in Copenhagen and helped negotiate with Sweden in Roskilde. In 1570, he helped complete the Peace of Stettin. After the death of ChancellorJohan Friis in December 1570, Kaas was appointed Chancellor by the Herredag in May 1573. In 1575, he became the second-most powerful person in the country on the death of the Steward of the Realm, Peder Oxe. Frederick II greatly relied on Kaas's negotiating skills. As chancellor, Kaas helped solve the question of succession for John II, Duke of Schleswig-Holstein-Haderslev and John II, Duke of Schleswig-Holstein-Sonderburg in 1582. He also served as the Chancellor of the University of Copenhagen, and under his leadership the university created its first professorship in history. Many of his writings survive from this time. He took special interest in the research of astronomy under Tycho Brahe, and of history in general. In June 1587 when Frederick II had toothache, Kaas met the Scottish ambassadors Patrick Vans and Peter Young who wanted to discuss the marriage of James VI to a Danish princess. Upon the death of Frederick II in 1588, Kaas became the guardian of government. During this time, he dealt with many issues, such as the influence wielded by the dowager queenSophia and her father Duke Ulrich III of Mecklenburg-Güstrow. Kaas was a supporter of the two, but the Folketing opposed their influence and sought to limit it. James VI married Anne of Denmark and came to Denmark in 1589 and gave Kaas a gold chain worth 900 dalers. On 12 December 1591 he signed the autograph book of Dietrich Bevernest, writing, "Fortuna fugacior undis." In 1593, Kaas helped emancipate the duchies of Schleswig-Holstein from the Holy Roman Empire and secure the rule over them of Frederick's successor, Christian IV. On his deathbed in 1594, Kaas called Christian IV in order to advise him on government, saying:
