François du Val, Marquis de Fontenay-Mareuil (fôNt′nā̇′mȧ′rẽ′y’) (c.1594-1665) was a French soldier, diplomat, and historian.

; served with Mayenne in Spain; with Nevers at Ratisbon; under Boisdauphin at the siege of Soissons (1617); in 1619 in Normandy; at Saint-Jean d'Angély, Clérac, and Montauban (1621); at Saint-Antoine and Montpellier (1622); at the Ile de Ré (1627); and at the sieges of La Rochelle (1628), of Privas, and of Alais (1629).

He announced the capture of La Rochelle to the Duke of Savoy; escorted Montpensier to the Court; negotiated with Rohan; and from 1630 to 1633 was Ambassador to England.

After taking part in various campaigns against the Imperialists and Spaniards, he was Ambassador at Rome from 1640 to 1650.

i., of the first series of the Collection Pettitot), are both interesting and valuable.