In 1570 Gilbert returned to England, where he married Anne Ager, daughter of John Ager ("alias" Aucher, etc.) of Otterden, who would bear him six sons and one daughter. In 1571 he was elected to the Parliament of England as a Member of Parliament for Plymouth, Devon, and in 1572 for Queenborough. Controversially he argued in favour of the crown prerogative in the matter of royal licenses for purveyance. In business affairs, he involved himself in an alchemical project with Smith, hoping for iron to be transmuted into copper and antimony, and lead into mercury.