French soldier who became a trusted servant of the British king William III.

Massue began his career as aide-de-camp to Marshal Turenne (1672–75), then went on diplomatic mission to England (1678). After the revocation of the Edict of Nantes (1685), Massue, a prominent Huguenot, along with his father and brother, settled in England in 1688. In 1690 he forfeited his French estates by entering the English army as major general of horse; he fought with distinction in the Irish campaign and was created Viscount Galway in 1692.

One of the few men absolutely trusted by William III, he was nevertheless resented among English politicians because of his foreign birth. In 1694 he was appointed to command the allied armies in Savoy, and in 1697 he received an earldom and was sent as lord justice to Ireland. Feeling unsuited to politics, he happily retired in 1701, but in 1704 he was called out of retirement to command the allied forces in Portugal during the War of the Spanish Succession. After a decisive defeat at Almansa (April 1707), he again retired, only to be recalled again to act as lord justice of Ireland (1715–16).