He and John Wotton especially distinguished themselves in rescuing from the enemy the dead body of the earl's brother, Walter Devereux, who had fallen into an ambush during a demonstration before Rouen.

[5] On the news being received of the siege of Calais by the Spanish, the Earl of Essex pushed to Dover; he wrote to Sir Anthony Shirley (3 April 1596) that he had sent Clifford to see whether he could ascertain the state of the town.

In August 1599, on coming to the Curlew Mountains, near Boyle, County Roscommon the baggage and ammunition were halted under the protection of the horse, while the infantry attempted the passage.

With the assistance of Hugh Roe O'Donnell's men, O'Rourke decisively defeated the English at Curlew Pass, and Clifford was left mortally wounded after being struck through the body with a pike.

Clifford's body was honourably buried at Holy Trinity Abbey, Lough Key and his "tragic death….was much lamented" by the Irish lords, as the man had "never told them a falsehood".

[4] In 1603, Clifford married Mary, daughter of Francis Southwell of Wymondham Hall, Norfolk,[2][4] and widow successively of Thomas Sydney of Kent and Nicholas Gorge.