Becoming a soldier, he was made a Knight of the Order of the Golden Fleece by Philip II, king of Spain, and was afterwards employed in diplomatic work.

After the death of his elder brother Charles II de Croÿ in 1551, he became 3rd Duke of Aarschot, 4th Prince of Chimay and 4th Count of Beaumont.

This attitude, together with Aarschot's devotion to the Roman Catholic Church, which he expressed by showing his delight at the Massacre of St. Bartholomew, led Philip of Spain to regard him with still greater favor, which, however, was withdrawn in consequence of Aarschot's ambiguous conduct when welcoming the new governor, John of Austria (Don Juan de Austria), to the Netherlands in 1576.

[1] Jealous of the Prince of Orange, he was then the head of the party which induced the Archduke Matthias (afterwards emperor) to undertake the sovereignty of the Netherlands, and soon afterwards was appointed Stadtholder of Flanders by the state council.

[1] He then sought to regain the favor of Philip of Spain, and having been pardoned by the king in 1580 again shared in the government of the Netherlands; but he refused to serve under the count of Fuentes when he became governor-general in 1594, and retired to Venice, where he died in December 1595.