In 1814 he was sent to Persia as minister plenipotentiary ad interim, and returned from that country in the following year, having successfully negotiated a treaty of peace.
Ellis reported that an impression could be produced at Beijing only by a knowledge of the military strength of the United Kingdom.
He took a job as deputy colonial secretary in the Cape of Good Hope in 1819, and was elected Member of Parliament for Boston in 1820, as a Tory.
The two positions proved incompatible, and after some delay his defeated opponent William Augustus Johnson had Ellis removed from parliament, in 1821.
He was despatched on a special mission to Brazil in August 1842, and at the close of 1848 he was appointed by the British government to attend the conference at Brussels on the affairs of Italy.