Rupert arrived in England to support his uncle, King Charles I, in the burgeoning conflict with Parliament. His military experience was immediately recognized, and he was quickly appointed commander of the Royalist cavalry.

Rupert led a successful cavalry charge at the Battle of Edgehill, the first major engagement of the war. However, his pursuit of the fleeing enemy allowed the Parliamentarian infantry to regroup, preventing a decisive Royalist victory. This set a pattern for his later victories and failures.

Rupert achieved a string of significant victories throughout 1643, including the capture of Bristol, a major port city. His aggressive tactics and charismatic leadership made him a popular figure among the Royalist troops.

Rupert commanded the Royalist forces at the disastrous Battle of Marston Moor. The defeat, largely attributed to poor coordination and the superiority of the Parliamentarian cavalry under Oliver Cromwell, marked a turning point in the war.

Rupert again commanded the Royalist cavalry at the Battle of Naseby, a decisive victory for the Parliamentarians. Despite initial successes, his cavalry once again pursued the fleeing enemy too far, leaving the Royalist infantry exposed. This battle effectively destroyed the main Royalist army.

Rupert surrendered Bristol to Parliamentarian forces after a relatively short siege. This surrender, viewed as premature by the King and many Royalists, led to his dismissal from command. He was accused of treason, though later cleared.

After a brief period of intrigue and attempts to regain favor, Rupert was forced to leave England following the surrender of Oxford, the Royalist capital. He went into exile on the European continent.