Born in Lisbon into a Portuguese Jewish family, he moved to the British colony of Virginia in 1745 and earned a living practising medicine.

[3] Sequeyra studied medicine in the University of Leiden beginning in 1736 and received his degree in 1739 with a dissertation entitled "De Peripneumonia vera", which he dedicated to his older brother "Joseph Henry de Siqueyra, M.D., physician to the Portuguese in the East Indies and chief physicist to the Viceroy of Goa".

In 1769, Colonel George Washington, as he was known then, frequently called in Dr. Sequeyra to treat his stepdaughter "Patsy," daughter of Martha Park Custis.

[5] John Custis IV, a Williamsburg resident, sent a letter to Peter Collinson, in 1741, inquiring about this thing called a "tomato".

[6] Thomas Jefferson himself informs us that introduction of the tomato as an edible fruit is due to the work of Dr. John de Sequeyra.