Rupert briefly served in the French army, though he was soon dismissed due to political tensions.

Rupert commanded a small Royalist naval squadron, engaging in privateering against English and other ships allied with the Commonwealth government. He aimed to disrupt trade and raise funds for the Royalist cause. His activities were often viewed as piracy by his enemies.

Rupert blockaded Kinsale, Ireland, and other ports, disrupting trade and supporting Royalist forces fighting in Ireland.

Rupert led his fleet to Portugal, seeking support from King John IV. He then sailed to the Mediterranean, engaging in further privateering and seeking alliances.

One of Rupert's primary ships, the "Constant Reformation", was lost in a storm off the coast of Africa, a significant blow to his naval capabilities.

After years of naval adventures, Rupert returned to France, having achieved limited success in disrupting Commonwealth trade but gaining a reputation as a daring and ruthless commander.

Rupert spent much of the late 1650s traveling across Europe. He continued to look for opportunities to serve the Royalist cause, as well as developed an interest in the arts and sciences.