In 1608 he was appointed Warden of the Forest of Dean, Constable of St Briavels Castle, Gloucestershire,[1] and in 1609 Governor of Portsmouth, all of which offices he retained until his death.

He was the eldest son and heir of Henry Herbert, 2nd Earl of Pembroke, of Wilton House, by his third wife Mary Sidney.

Herbert was a bookish man, once tutored by the poet Samuel Daniel, and preferred to keep to his study with heavy pipe-smoking to keep his "migraines" at bay.

[7] In 1597, his father negotiated a marriage between Herbert and Bridget de Vere, a granddaughter of William Cecil, 1st Baron Burghley.

E. K. Chambers, who had previously considered Henry Wriothesley, 3rd Earl of Southampton to be the Fair Youth, changed his mind when he encountered the evidence in letters that Herbert had been urged to wed Elizabeth Carey.

A life-size bronze standing statue of William Herbert, 3rd Earl of Pembroke, was sculpted by Hubert Le Sueur (c. 1580-1658) and stood at the family seat of Wilton House, Wiltshire.

[11] The square stone plinth is inscribed on two sides in Latin: Gulielmus Pembrochiae Comes regnantibus Jacobo et Carolo Primis hospitii regii camerarius et senescallus Academiae Oxoniensis Cancellarius munificentissimus ("William, Earl of Pembroke, Chamberlain and Steward of the Royal Household in the reign of James I and Charles I, and most munificent Chancellor of the University").

On the opposite side: Hanc patrui sui magni effigiem ad formam quam tinxit Petrus Paulus Rubens aere fuso expressam Academiae Oxoniensi d(edit) (et) d(edicavit) Thomas Pembrochiae et Montgom(eriae) Comes honorum et virtutum haeres A.D. MDCCXXIII ("Thomas, Earl of Pembroke and Montgomery, inheritor of his titles and qualities, gave and dedicated to the University of Oxford this statue of his great-uncle cast in bronze in the form that Peter Paul Rubens had painted.