A military man who served in James I's army in the Palatinate in 1624. He then entered the service of the Netherlands and was Colonel of an English Regiment serving in Holland. Late in 1648 when news of the condemnation to death of Charles I was received, he was sent by the Prince of Orange to his cousin Oliver to plead for the King's life. Having with difficulty gained admittance, he argued vehemently that the execution would be seen on the Continent as an indelible stain on England and even threatened Oliver that the entire family would change their name back to Williams out of shame if the execution went ahead. The mission was, of course, unsuccessful, and John Cromwell returned to Holland. He saw the conduct of his cousin as criminal, though that didn't stop him applying to the Lord Protector for redress over a case involving his estranged wife who had, he claimed, reduced him to penury.