He served as ensign at Maastricht since 1672; after the siege of that fortress a year later, the Prince of Waldeck promoted him to captain as a reward for his brave conduct.

William III of Orange, promoted him to lieutenant-colonel and captain of the Dutch Blue Guards and in 1679 to colonel of the Lavergne regiment, after participating in four campaigns.

Fagel achieved greater fame in 1691 by defending Mons, under the supreme command of the Prince of Grimberghen, against close to 100,000 Frenchmen under Boufflers and Vauban; due to civilian pressure, the city was surrendered in spite of the strong resistance of the garrison.

At the storming of Liège, it was the Dutch, English and Prussian battalions, under Fagel and Somerfield, who decided the battle in favour of the Allies.

At the Siege of Bonn under the leadership of Menno van Coehoorn, Fagel was one of the sub-commanders, with Obdam, Dedem and Pallandt.

Lack of support and co-operation, inexperienced troops, badly trained cavalry, opposition from the local population and pro-French Spanish statesmen forced him to abandon the Siege of Badajoz; regretting this, he asked to be recalled, but for the time being remained in Iberia.

During that battle he, together with the Prince of Orange, led the infamous Dutch assault which caused enormous casualties among them.

Marlbourogh refused any negotiations, so that Bouchain, which was under the command of de Ravignan, had to surrender on mercy or disfavour and its garrison thus became prisoners of war.