Can a peasant marry a member of the nobility or royalty?

1st Answer:

No.

2nd Answer:

There was no restriction in law, secular or religious, except for extraordinary circumstances. I cannot think of a case of a peasant who married an important member of the nobility, but I can think of other commoners who did.

Emperor Justinian I of the Byzantine Empire was already a very important man when he married Theodora. She was an actress, and is said to have been raised in a brothel and to have been involved in pornographic productions on stage. She was not a peasant, but socially a lot of people would have put her at a level below that of a peasant.

Owen Tudor was not a member of the nobility when he became steward to Queen Catherine of Valois, who was the widow of King Henry V and the mother of King Henry VI. They married illegally, because it was illegal for the mother of a minor king to marry without permission of parliament, but no one seems to have cared much. The law was intended to prevent a powerful faction from gaining power over a young king, and Owen Tudor had no power to worry about. They had several children together, and two were given titles by Henry VI. One of these was the Earl of Richmond, and was the father of a son named Henry, who became King Henry VII.