Guillaume-Hugues d'Estaing was born in Étain, the son of Hugues d'Estaing.^[1] After becoming a doctor of both laws, he entered the Order of Saint Benedict.^[1] He was ordained as a priest and then became archdeacon of Verdun.^[1] He later became archdeacon of Metz.^[1]

He was in attendance at the Council of Basle (1431–43).^[1] In 1437, he was a member of the conciliar commission that reported on the poor governance of the church by Pope Eugene IV.^[1] In the papal conclave of 5 November 1439 he was one of the supporters of Antipope Felix V.^[1]

Antipope Felix V made him a pseudocardinal on 6 April 1444 in Geneva, offering him the titular church of San Marcello al Corso.^[1] Estaing refused Felix V's offer to make him a cardinal, instead choosing to side with Pope Nicholas V, who absolved him for his earlier support of Felix.^[1] In the consistory of 19 December 1449, Nicholas V made Estaing a cardinal priest, awarding him the titular church of Santa Sabina on 12 January 1450.^[1] Estaing entered Rome on 30 November 1450 and received the red hat the next day.^[1]

On 1 March 1451, he was elected Bishop of Sion, though a dispute with the cathedral chapter ultimately led to his resignation as bishop on 11 September 1454.^[1] He was present at the secret consistory of 27 October 1451.^[1] He served as Camerlengo of the Sacred College of Cardinals from November 1452 to 5 November 1453.^[1] On 27 June 1453, he was elected Bishop of Fréjus, holding this position until his death.^[1] He participated in the papal conclave of 1455 which elected Pope Callixtus III.^[1]

He died in Rome on 28 October 1455.^[1] He is buried in Santa Sabina.^[1]