Henniker too became a merchant dealing in leather and furs. He was also involved in politics and was appointed High Sheriff of Essex for 1758 before being elected to the House of Commons for Sudbury in 1761. He held that seat until 1768, and then represented Dover from 1774 to 1784.
He was elected a Fellow of the Royal Society in 1779.
In 1782, Henniker succeeded his father-in-law as second Baronet of Worlingsworth Hall according to a special remainder. In 1800 he was raised to the Peerage of Ireland as Baron Henniker, of Stratford-upon-Slaney in the County of Wicklow.
Lord Henniker died in April 1803, aged 78, and was buried in Rochester Cathedral. Sir Brydges Trecothic Henniker, became a Lieutenant-General in the Army and was created a Baronet in 1813.
The town of Henniker, New Hampshire, was named after Lord Henniker.
Royal Society; 12th Parliament of Great Britain. 14th Parliament of Great Britain. 15th Parliament of Great Britain.