Major William Rainsborowe, or Rainborowe, was an officer in the English Navy and New Model Army in England during the English Civil War and the Interregnum. He was a political and religious radical who prospered during the years of the Parliamentary ascendancy and was an early settler of New England in North America.

Captain William Rainsborough, usually spelt Rainsborowe, was an English Captain and Vice-Admiral in the Royal Navy, English ambassador to Morocco and politician who sat in the House of Commons from 1640 to 1642.