Long was a friend of William Pitt the Younger, whom he had met at Cambridge, and his involvement in politics began as early as 1788 when he was canvassing for Lord Hood, the ministerial candidate in the Westminster election,[citation needed] and he himself entered parliament in January 1789 as member for Rye,[2] a Treasury controlled seat.

He afterwards sat as member for Midhurst (1796–1802)[3] and for Wendover (1802–06),[4] (boroughs whose parliamentary representatives were nominated by Pitt's friend Lord Carrington) and for Haselmere (1806–26),[5] where the sole patron was the Pittite Earl of Lonsdale.

In 1792 with Sir James Bland Burges, Long established the Sun newspaper as an instrument of the Tories, and he was the author of pamphlets on the French Revolution (1795) and the price of bread (1800).

In 1820 King George IV made Long a Knight of the Bath, and on his retirement from political life in 1826 he was raised to the peerage as "Baron Farnborough, of Bromley-Hill-Place, in the county of Kent".

The arts were Long's real passion, but due to limited resources he was unable to be a major patron or collector in his own right, however, as a minister and MP he was influential in furthering artistic causes such as the establishment of the National Gallery and the purchase of the Elgin marbles, and was a founder of the British Institution in 1805.

He acted as intermediary in 1792 between Pitt and Humphry Repton over improvements to the former's grounds at Holwood, and in 1799 when the Altieri Claudes were brought to England, they were first exhibited to English connoisseurs at Long's house in Grosvenor Place.

A committee of taste was appointed in 1802 to supervise the erection of monuments to the heroes of the Napoleonic wars, of which Long was chairman, and in 1809 the responsibilities were extended to the repair of Henry VII's chapel at Westminster, with money voted by parliament.

Long was consulted on everything from the need for a fig-leaf on the heroic statue honouring the Duke of Wellington, that had been subscribed for by the ladies of Great Britain (1821), to the appropriate order for the facade of the privy council offices in Whitehall (1824).

The extensive grounds were progressively improved to create a much-admired garden which by 1809 offered two picturesque walks, each a mile long, and a distant view of the dome of St Paul's Cathedral.