The Honourable Topham Beauclerk was the only son of Lord Sydney Beauclerk, and a grandson of the first Duke of St. Albans. He was born in 1739, and on the death of his father in 1744 succeeded to the estates which Lord Sydney had inherited from Mr. Richard Topham, M.P. for Windsor. In 1757 Beauclerk matriculated at Trinity College, Oxford, but seems to have left the University without taking a degree. While he was at Oxford he made the acquaintance of Dr. Johnson, who appears to have been greatly attracted to him on account of his wit and conversation. This intimacy surprised many of Johnson's friends, for although Beauclerk valued science and literature, he was also gay and dissipated. 'What a coalition,' said Garrick, when he heard of it, 'I shall have my old friend to bail out of the Round-house.' Notwithstanding somewhat frequent squabbles, the friendship lasted for upwards of twenty years, and on Beauclerk's death Johnson remarked of him—'that Beauclerk's talents were those which he had felt himself more disposed to envy, than those of any whom he had known.'[84] His conversational powers were evidently of a very high order, for Dr. Barnard, Bishop of Limerick, in his well-known lines on Dr. Johnson, writes of him:

'If I have thoughts, and can't express 'em,
Gibbon shall teach me how to dress 'em
In terms select and terse;
Jones teach me modesty and Greek;
Smith, how to think; Burke, how to speak;
And Beauclerk to converse.'

Beauclerk married on the 12th of March 1768 Lady Diana Spencer, eldest daughter of the second Duke of Marlborough, two days after her divorce from Lord Bolingbroke and St. John. He died at Great Russell Street, Bloomsbury, on the 11th of March 1780, leaving one son and two daughters.

Beauclerk possessed a fine library of upwards of thirty thousand volumes, which he kept at his residence at Muswell Hill, near London, stored, as Horace Walpole informs us, 'in a building that reaches half-way to Highgate.' It did not contain many rare books, but it was rich in works relating to natural history, voyages and travels, and English and French plays; and Dibdin says that it was also valuable to the general scholar, and to the collector of English antiquities and history. It also possessed a few curious and choice manuscripts. Some of the books appear to have belonged to Mr. Topham, but most of them were collected by Beauclerk. After his death they were sold by auction by Mr. Paterson 'at the Great Room, heretofore held by the Society for the Encouragement of Arts and Manufactures, opposite Beaufort Buildings, in the Strand, London,' on Monday, April 9th, 1781, and the forty-nine following days. A priced copy of the catalogue is in the British Museum.

Beauclerk, who was a Fellow of the Royal Society, was a collector of natural curiosities, as well as books, and botany was one of his favourite studies. He had also an observatory at Muswell Hill.