Robert Devereux, the eldest son of Robert Devereux, 2nd Earl of Essex, was born in 1591. Devereux's father was executed for treason by Elizabeth in 1601. However, in 1604 James I restored Devereux to his father's estate.
Devereux served under the Duke of Buckingham in the expedition against the Spanish at Cadiz in 1625. The following year he became associated with the opposition to Charles I. He refused to pay the forced loans demanded by the king in 1627 and in 1628 voted for the Petition of Right which criticized royal conduct of government.
Devereux's military leadership was criticised by Henry Vane, the political leader of the House of Commons. Devereux fought back by trying to have Oliver Cromwell impeached for sedition. This move failed and in April 1645 he joined Edward Montagu, Earl of Manchester, in resigning from the army.
Robert Devereux, 3rd Earl of Essex, died in September, 1646.