Kaas spent the 20 first years of his career in Norway, then part of
Denmark-Norway. In 1782, he became a judge at the Norwegian
Overhofret. In 1787 he left the post to focus on the management of
Bærum Ironworks, which he had acquired through his marriage to Kirstine Nilson. In 1789–90, he was a Supreme Court justice for Denmark-Norway. In 1789, he returned to the Norwegian
Overhofret. In 1790, he was appointed to the post as associated
lagmand of Akershus lagdømme. In 1792–94, he was chairman of the City Council in
Kristiania. In 1794, he became auditor-general and member of the Norwegian Gneralitets- og Kommissariatskollegium. From 1795 to 1802, he served as
diocesan governor of Akershus. In 1802, Kaas was called back to Copenhagen and Denmark to serve as president of the Supreme Court for Denmark-Norwway.
Gebgard Moltke replaced him as diocesan governor of Akershus. In 1804, Kaas became president of the
Danske Kancelli. In 180910, he was temporarily back in Norway. In 1811 and 1813, and he was sent on diplomatic missions to Paris. In 1814, he was made a member of the
Heheimestaten, In 1813, he was given title of Minister of Justice. In 1815, he was also appointed to the post as head of the Copenhagen Police Force, concurrently to his posts as Minister of Justice and president of Danske Kancelli. Kaas was also made a member of a number of important commissions. Outside the central administration, Kaas was appointed as one of the directors of the
Classenske Fideicommis, in 1802, and, in 1705, as president of
Herlufsholm School. He was also active in the management of Ordenskapitlet, first as vice chancellor (1808) and then as chancellor (1825). In 1805, he was created an honorary member of the Royal Society for Ancient Nordic Manuscripts (
kgl. nordiske oldskriftselskab). In 1808, he was also made an honorary member of the
Royal Danish Academy of Fine Arts. He was created a
White Knight in 1803 and a
Blue Knight in 1815. ==Personal life==