He was only five when he lost his father, making him heir to his grandfather, the 2nd Duke of Grafton. However, he had to wait until 1757, at twenty-two, to succeed his grandfather and become 3rd Duke of Grafton. He was educated at Westminster, made the Grand Tour, and
obtained a degree at Cambridge. The year before he became Duke of Grafton he married the Hon. Anne Liddell, daughter of Lord Ravensworth, and they became the parents of three surviving children.
After his marriage he entered politics and became M.P. for Bury St.Edmunds as well as Lord of the Bedchamber to the Prince of Wales. However, most of his time was spent fox-hunting and racing. He admired William Pitt (the Elder) and when, in 1765, he was made Secretary of State in Lord Rockingham's government, he did all he could to pursuade Pitt to join the administration. As Pitt objected to another member of the government, the Duke of Newcastle, he declined.
A few months later Grafton resigned because he wished that Pitt would join the government and without himself he expected the government would fall, which it subsequently did. Pitt became Prime Minister and Grafton was given the Treasury. However, when under pressure, Pitt had spells of madness and, as a consequence, Grafton became Prime Minister in March 1768, but was soon exposed as weak and ineffectual while at the same time it was known by society that his wife was with child by the Earl of Upper Ossory. Even though he himself had Nancy Parsons as mistress, he divorced his wife.
Daughter of a Bond Street tailor, Nancy Parsons had lived with a slave-trader and after him called herself Mrs. Horton. She became known as "The Duke of Grafton's Mrs. Horton, the Duke of Dorset's Mrs. Horton, everybody's Mrs. Horton". However, as Prime Minister he flaunted her, even in the presence of the Queen. As well as the time spent with Nancy Parsons, he went to the races and hunted foxes.  "Pretty occupations for a man of quality," said the King, "to be spending all his time tormenting a poor fox that is generally a much better beast than any of those that pursue him." However, Horace Walpole put it differently, "thinking the world should be postponed to a whore and a horse race".
In 1769 he married Elizabeth Wrottesley who was "not handsome, but quiet and reasonable". They lived happily together for forty years and produced some seven or more children. In 1770 Grafton resigned as Prime Minister, which the King regarded as desertion. He supported North's government until 1775 when he found the policy towards the American colonies more than he could stomach. In 1783 William Pitt (the Younger) formed a government but Grafton refused a third term as Lord Privy Seal. The King gave him the Garter.
He retired to the country, collected books and took up theology till he died in 1811, aged seventy-seven.
 

Source: Leo van de Pas