MACNAGHTEN, SIR WILLIAM HAY (1793-1841), born in August 1793, was the son of Sir Francis Macnaghten. He was educated at Charterhouse and joined the service of the East India Company in 1809. He studied Hindustānī, Persian and other Asiatic languages. His diplomatic career began towards the close of 1830, when he accompanied Lord William Bentinck as secretary on his tour through the upper and western provinces of India. He was also present at the Governor-General's meeting with Mahārājā Raṇjīt Siṅgh at Ropaṛ in October 1831. Returning to Calcutta, he was appointed to take charge of the secret and political departments and held that post for four years. In 1838, he headed a mission to the Sikh capital which led to the signing, on 26 June 1838, of the Tripartite treaty.

         Macnaghten's mission to Lahore was undertaken in view of the growing Russian influence in Persia and Afghanistan and the supposed threat to the British possessions in India. Auckland's government had decided to subvert the power of Amīr Dost Muhammad Khān and to restore ex-king Shāh Shujā’ to the throne at Kābul with the help of Sikh arms and British money. Mahārājā Raṇjīt Siṅgh was agreeable to Macnaghten's proposals, but laid down certain conditions. Among other things, he demanded a perpetual tribute or subsidy of 2,00,000 rupees to be paid annually by Afghanistan to the Sikhs, a compensation for forgoing claims on Shikārpur and Sindh, and the cession of the district of Jalālābād and its dependencies to him. All the demands of the Mahārājā except the cession of Jalālābād were agreed to by Macnaghten.

         After the restoration of Shāh Shujā' in 1839 in which the Sikh forces did not take part in any military operations beyond the Khaibar, Sir William was appointed the British minister and envoy to Kābul. Amidst mounting disagreements between the Sikhs and the English, particularly on the Sikh-Afghān borders and the two frontier territories of Swāt and Buner, Macnaghten made wild accusations against the Sikh Darbār. He demanded the recall of the Sikh governor of Peshāwar, General Avitabile, who, he alleged, was coercing the Khaibarīs and extending Sikh influence beyond their borders. He complained that the Peshāwar Bārakzaī tributaries of the Sikh government were giving asylum to the Gilzaic chiefs, the rebel Afghān subjects. Macnaghten finally contended that after the death of Raṇjīt Siṅgh, the Tripartite treaty had lapsed and proposed that the Sikhs restore to the Afghāns their former territories on the Indus, including Peshāwar.

         On 23 December 1841, Sir William Macnaghten was lured by the Afghāns into a conference and assassinated by Prince Akbar Khān, the deposed Amīr's son.