Мальмёхус
Posse was born at Rosendal manor in Malmöhus County, as the son of Governor Count Fredrik Posse and Baroness Magdalena Charlotta Bennet. In 1835 he enrolled at Lund University, receiving a law degree in 1840. The same year, he began as a trainee at the Court of Appeal of Skåne and Blekinge ("Hovrätten över Skåne och Blekinge"), during which time he worked both at district courts and at the Court of Appeal itself. Later, he was appointed assistant district judge ("vice häradshövding") and in 1846 a clerk at the Court of Appeal, and in 1847 was made an associate justice at the court. In 1849 Posse left public service and resettled at Charlottenlund Manor and devoted his time to agriculture, enterprise and local politics (being, e.g., 1865–68 the president of Malmöhus County Council).