Frederick William succeeded his uncle on 21 June 1692 as regent of the Schwerin portion of the duchy of Mecklenburg.

It brought the country to the brink of civil war and was settled only through the intervention of foreign powers.

The king of Denmark and Norway, Frederick IV, gave up the inheritance request for the Mecklenburg-Güstrow principality in exchange for the Duke's support for Denmark-Norway in the Great Northern War.

In addition to the taxation of knights and the clergy, this law included the abolition of serfdom, freeing farmers from dependence on their landlords.

Frederick William had numerous mistresses, with whom he had at least nine children, including: A lady named Frederika Wilhelmina was born in 1702 in Boitzenburg[2] and died 1748 in Schwerin.