Thornborough was born in Salisbury, and graduated from Magdalen College, Oxford.

In a long ecclesiastical career, he was employed as a chaplain by the Earl of Pembroke, and Queen Elizabeth.

[1] He was appointed Clerk of the Closet in 1588, serving Queen Elizabeth I in that capacity until the end of her reign in 1603.

[2] He also shielded the future biographer Samuel Clarke (1599–1683).

[5] Robert Fludd dedicated Anatomiae Amphitheatrum (1623) to Thornborough.