In 1610 Carew was appointed Governor of Guernsey. He visited Ireland to report on prospects for a settlement and plantation of Ulster, and discovered rapid improvements and recovery in the country. He also suggested the creation of new boroughs in the northern province, in order to ensure a Protestant majority in the forthcoming parliament, a suggestion that was successfully adopted in 1613. He became a privy councillor in 1616. In 1618 he pleaded to the crown for the life of Sir Walter Raleighthey had been intimate for 30 yearsand his wife was a kind friend to the family after Raleigh's execution.