In a contract of inheritance dated 1619, Francis Henry recognized his elder brother Augustus as sovereign, in exchange for an annual appanage of 2500 thaler.
When King Gustav II Adolf of Sweden landed in Peenemünde in 1630, Francis Henry entered his service and earned his affection.
When his brother Augustus died, Francis Henry received Wangelau and Rothenbeck (a part of today's Grande) in addition.
While in Swedish service and thereafter he spent a lot of time with Sophia of Schleswig-Holstein-Sonderburg (1579–1658), dowager of Philip II, Duke of Pomerania.
It was at her dower in Treptow upon Rega, a former nunnery which she had converted into a castle, where Francis Henry and Marie Juliane of Nassau-Siegen (1612–1665) married on 13 December 1637.