Son of William Pepys (ca. 1698-1743) and Hannah Weller Russell (d. ca. 1760). Married (1777) to Elizabeth Dowdeswell, daughter of Right Hon. William Dowdeswell of Pull Court (d. 1775). Educated at Eton and at Christ Church, Oxford. Master in the High Court of Chancery. An intimate friend of James Macdonald. A sometime friend of Henry and Hester Thrale. Pepys was created a baronet in 1801.
One of William and Elizabeth's sons, Charles Christopher Pepys, became Solicitor General (1834), High Commissioner of the Great Seal (1835) and Lord High Chancellor (1836-41 and 1846-50).
Boswell met William Pepys in the company of James Macdonald during his visit to the latter in Oxford, April 23-26, 1764.
It is possible, however, to find rather inexpensive editions of A.C.C. Gaussens A Later Pepys (The Correspondence of Sir William Weller Pepys) via the AbeBooks used books search engine. Included is his correspondence with, among many others, Sir James Macdonald.
Samuel Pepys, Boswell's predecessor as a master diarist, is a distant relation of William Pepys'.