He attended Magdalene College, Cambridge where he read law; afterwards he studied for the Bar, and was called by the Middle Temple in 1864.
Developing the family newspaper business, Cox also became proprietor of The Field, and also edited the annual Angler's Diary under the initials "I.E.B.C.".
When the sitting Member of Parliament for Harrow, William Ambrose, was appointed a Judge, Cox was unanimously selected to follow him.
Cox was a self-described "strong supporter of Mr. Balfour's government", and he also went along with Joseph Chamberlain's campaign for tariff reform.
However, Cox did not entirely enjoy Parliamentary life; although re-elected at the 1900 general election, no speech by him in the House of Commons is recorded.