In 1455 Edmund married the young Margaret Beaufort who was descended though the Lancastrian line from Edward III. This was the period of history known as the Wars of the Roses between two sets of descendants of King Edward III who both fought for control of the English throne. Edmund was captured by the Yorkists and died in captivity in 1456. Jasper took Edmund's wife Margaret Beaufort who was expecting their first child to Pembroke Castle for safety. It was at Pembroke Castle that Margaret's child, Henry Tudor, was born. Henry would later become Henry VII, King of England.
During the 1460s Jasper was a keen Lancastrian supporter and supported Queen Margaret's attempts to restore her husband King Henry VI to the English throne. Eventually he left England for France and in 1468 received financial assitance from King Louis XI of France who provided money for an invasion of England. The small invasion force landed in Wales and captured Denbigh, but Jasper had to flee when an English army retook the town. In 1470 Jasper was a member of a more successful invasion led by Warwick the Kingmaker that managed to restore King Henry VI to the throne, but the victory was short-lived. A year later the Lancastrians were defeated at the battles of Barnet and Tewkesbury and Japser was forced to flee England. This time he took with him his nephew, the young Henry Tudor, and they ended up in Brittany where they were given refuge. There they stayed relatively safe from Edward IV, the Yorkist king in England.
In 1483, after the death of Edward, Richard III became king of England by possibly arranging the disappearance and deaths of Edwards young sons in the Tower of London. Two years later a new invasion was planned and executed resulting in the death of Richard at the Battle of Bosworth. With the help of his uncle Jasper, Henry Tudor became king as Henry VII. In 1485 Jasper married Catherine Woodville, the daughter of Richard Woodville, 1st Earl Rivers and Jacquetta of Luxembourg but they had no children.