He was in correspondence with Sir Hans Sloane by 1724 sending him, among other things, 'two carps from Norway'.
Sloane proposed Theobald as Fellow of the Royal Society,[2] and he was duly elected in November 1725.
Theobald was an active member of the Royal Society, proposing more than 30 Fellows during the rest of his life.
Later in life, Theobald was a Director of the Bank of England (1743-1756), Master of the Barber-Surgeons company (1750) and governor of the Merchant seaman's corporation.
His collection of 'shells, fossils, pictures, specimens of penmanship, coins and medals in gold, silver and brass, and various other articles' was sold by auction in Covent Garden in June 1768.