| Constituency | Dates |
|---|---|
| St Germans | 1780 – 1784 |
| Great Grimsby | 1784 – 11 Apr. 1793, 17 Apr. 1793 – 96 |
| Banbury | 1796 – 06, 1807 – 1812 |
| Newtown I.o.W. | 1807 – Feb. 1808 |
| Banbury | 16 Feb. 1808 – 12 |
| Richmond | 1812 – 1818 |
| Haddington Burghs | 1818 – 20 |
| Newtown I.o.W. | 1820 – 1 Feb. 1821 |
Long was a friend of Lord Richard Cavendish, and in 1780 was recommended by Rockingham to Edward Eliot who brought him into Parliament.1Rockingham to Portland, 1 Sept. 1780, Portland mss. In 1784 he was returned for Grimsby on the interest of Charles Anderson Pelham, his future father-in-law. He voted with Fox and formed one of the nucleus of his party. He was a manager for the impeachments of Hastings and Impey.
Dr. Johnson’s comment is well known:2Boswell, Johnson, iv. 81. ‘Long’s character is very short. It is nothing. He fills a chair. He is a man of genteel appearance and that is all.’ But Boswell adds: ‘Little did he know that, owing to Mr. Long’s reserve in his presence, he was talking thus of a gentleman distinguished among his acquaintance, for acuteness of wit.’ George Crabbe, the poet, whom Long befriended when poor and unknown, wrote of him:3Life and Works (1854), pp. 13, 43.‘Though a silent Member of the House (for he had a strong impediment in his utterance), “yet”, said Mr. Fox, “we owe to Dudley’s suggestions some of the best hits we have made”.’
Long died 21 Feb. 1829.