He ruled as an enlightened despot, and raised money by renting soldiers (called "Hessians") to Great Britain to help fight the American Revolutionary War.

He combined Enlightenment ideas with Christian values, cameralist plans for central control of the economy, and a militaristic approach toward international diplomacy.

His education was initially entrusted to Colonel August Moritz von Donop and then from 1726 to 1733 to the Swiss theologian and philosopher, Jean-Pierre de Crousaz.

On 8 May 1740, by proxy in London, and on 28 June 1740 in person in Kassel, Frederick married Princess Mary, fourth daughter of King George II of Great Britain and Caroline of Ansbach.

They had four sons: In December 1745, Frederick landed in Scotland with 6000 Hessian troops to support his father-in-law, George II of Great Britain, in dealing with the Jacobite rising.

The younger sons lived permanently in Denmark, rising to high office in the court of their cousin; only William returned to Germany upon inheriting the principality of Hanau.