There are short biographical notes of Dunthorne, one in the Philosophical Transactions (Abridgement Series, published 1809) (unsigned), another in the , and a third by W T Lynn. Dunthorne was born in humble circumstances in Ramsey, Cambridgeshire, where he attended the free grammar school. There he attracted the notice of Roger Long (later Master of Pembroke Hall, Cambridge), whose protégé Dunthorne became. Dunthorne moved to Cambridge where Long first appointed him as a "footboy", and where he received some further education (though this does not seem to have been regular university education). Dunthorne then "managed" a preparatory school in Coggeshall, Essex, and later returned to Cambridge where Long obtained for him an appointment as a "butler" at Pembroke Hall, an office that Dunthorne retained for the rest of his life. Here Dunthorne's main activity seems to have been in assisting Long in astronomical and scientific work.