John Proby was the son of John Proby and Jane Leveson-Gower. He graduated from Cambridge University in 1741. In 1747 he became the MP for Stamford and held the seat until 1754 when he became MP for Huntingdonshire which he held until 1768.
In 1750 John married Elizabeth Allen, daughter of Joshua Allen, 2nd Viscount Allen and Margaret du Pass. A few years later he was created 1st Baron Carysfort, of Carysfort, co. Wicklow, Ireland, in 1752. He seems to have become involved in some capacity with the Board of the Admiralty in 1757 and then from 1763 to 1765.
He is mentioned briefly in the diary (page 110) of George Marsh in May 1764. George notes that he set out with Lord Egmont, Lord Howe and Lord Carysford with Mr Stephens to visit the Dockyards.
John died on 18 October 1772 at age 51 at Lille, France and was buried at Elton, Huntingdonshire, England.
(George Marsh) (Diary of George Marsh)