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).
Lethieullier subsequently travelled in France, Italy, Germany, and throughout Britain, and developed a passion for the study and collection of antiquities and fossils.
He developed a wide network of antiquarian and scientific friends and contacts, including Francesco Ficoroni, Bernard de Montfaucon, Richard Pococke, Andrew Ducarel, Francis Wise, Martin Folkes, Samuel Gale, Richard Mead and Peter Collinson.
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.