Lethieullier was born on 3 November 1701 at Aldersbrook Manor House, Little Ilford, Essex. His family was of Spanish Netherlands Huguenot origin, and had come to London as refugees in 1605. His grandfather, Sir John Lethieullier (1632/3–1719), had succeeded in trade, and had risen to become Sheriff of London in 1674–5, and owner of the Aldersbrook estate (purchased 1693). Sir John's son, also named John (d. 1737), married Elizabeth Smart, and Smart was their second son. He was educated at Eton College and Trinity College, Oxford, from where he graduated MA in 1723.
He wrote numerous letters and papers on antiquarian topics. None were published in his lifetime, but a number appeared posthumously in Archaeologia (journal of the Society of Antiquaries) and elsewhere. His subjects included Roman remains (including those in the grounds of Wanstead House and neighbouring Aldersbrook Manor), the Ambresbury Banks hillfort, the shrine of St HughinLincoln Cathedral, and techniques for the dating of English church monuments. In 1732–33, when he was living in Paris, he wrote the first detailed account in English of the Bayeux Tapestry: it was eventually published in 1767 as an appendix to Andrew Ducarel's Anglo-Norman Antiquities.[1][2]
In 1737, on his father's death, Lethieullier inherited Aldersbrook and began to improve the grounds, including the building of a hermitage in which to house his collections.
Lethieullier married Margaret Sloper in February 1726. She died in 1753: there were no children of the marriage. His estates were inherited by his niece Mary, daughter of his younger brother Charles.
