Knyphausen was from Lütetsburg, East Frisia. He learnt his trade in Dutch service under Maurice of Orange, rising to the rank of captain by 1603. He later served the Hanseatic League, then the Protestant Union. In the 1620s, with the Thirty Years' War turning against the Protestants, Knyphausen had the misfortune to be repeatedly on the losing side, witnessing the defeats at the Battle of Höchst (1622) and the battle of Stadtlohn (1623). After the latter battle he was accused of treason and even sentenced to death, only to be exonerated. He fought under Ernst von Mansfeld at the Battle of Dessau Bridge in 1626, but was captured. In 1628 during the siege of La Rochelle, he went into English service and raised troops, during the final abortive English attempt to relieve the Huguenot stronghold.