Cage was the son of William Cage, lawyer of Hollingbourne, Kent and his wife Cicely Culpeper, daughter of Sir Cheney Culpeper and Elizabeth Stede.
He was High Sheriff of Kent in 1694 but was fired from the justice's bench in December 1695 and arrested in February 1696 for betraying confidants.
[2] At the 1701 election, Cage stood for parliament at Rochester but was unsuccessful as a result of a smear campaign under the allegations of disloyalty.
However, he was elected Member of Parliament (MP) for Rochester in 1702 and sat until 1705 when following his defeat he was described as a "violent man".
He was re-elected for Rochester again in 1710 in a Tory landslide and sat until 1715 when he declined to stand.