In a long ecclesiastical career, he was employed as a chaplain by the Earl of Pembroke, and Queen Elizabeth. He was Dean of York, Bishop of Limerick in 1593, Bishop of Bristol in 1603, and Bishop of Worcester from 1617. He also shielded the future biographer Samuel Clarke (1599–1683).
He wrote an alchemical book, Lithotheorikos of 1621.
He is known to have employed Simon Forman. Robert Fludd dedicated Anatomiae Amphitheatrum (1623) to Thornborough.