Methuen went to
Lisbon in 1691, when his father was appointed minister there. He gained valuable diplomatic experience and the esteem of
Peter II of Portugal. During two absences of his father, he became
chargé d'affaires, rising to Minister on his father's appointment as
Lord Chancellor of Ireland in 1697. He was unable to prevent a Portuguese-French alliance in 1701. When his father returned to
Portugal as a special envoy in 1702, they were successful in breaking the alliance in 1703. That led to the
Methuen commercial treaty between
England and Portugal, the basis of Britain's monopoly of Portuguese trade for much of the 18th century. His father remained in Portugal as ambassador. In 1705, Methuen served with the army, being present at the capture of
Gibraltar. On his return to England to obtain military supplies he was appointed
Minister to
Savoy, but succeeded his father as ambassador to Portugal on the latter's death in July 1706. While he was in Portugal, the
Kingdom of England became the
Kingdom of Great Britain following the ratification of the
Acts of Union 1707, resulting in Methuen becoming the first
ambassador of Great Britain to Portugal. ==Political career==