His murder by Jörg Jenatsch marked a key Protestant (and anti-Habsburg) uprising in Graubünden during the Thirty Years War.

As a member of the important Planta family, he soon found himself in high office: in 1614 he was bailiff of the Bishopric of Chur in Fürstenau, as well as Hereditary Marshal.

Together with his older brother Rudolf, he led the movement for the Three Leagues to support the Austro-Spanish party.

In 1618, his opponents of the Franco-Venetian Party outlawed the Planta brothers and sentenced them to death.

On 25 February 1621, Pompeius was murdered in the presence of his daughter Catherina at Rietberg Castle in Domleschg by a group led by his opponent Jörg Jenatsch.