After the death of his father in 1556 he was raised at the court of his guardian and uncle, the Protestant Count Hermann of Neuenahr and Moers, who was married to Magdalene, a half-sister of William the Silent, Prince of Orange.

In 1570 he married his aunt Walburgis van Nieuwenaer, the widow of Philip de Montmorency, Count of Hoorn who had been executed by the Duke of Alba in 1568.

When Count Hermann died childless in December 1578, Niewenaar inherited his lands, including the county of Moers.

Gebhart was supported by Nieuwenaar (as his general), his brother, Karl, Truchsess von Waldburg-Trauchburg and the Dutch rebels.

The stadtholder of the province of Gelderland in the States-General, Willem IV van den Bergh, had been caught in treasonous correspondence with the Spanish Governor-General of the Habsburg Netherlands, Alexander Farnese, Duke of Parma, and had been deposed in November 1583.

[2] In 1585, the Spanish general Juan Baptista de Tassis defeated him and Maarten Schenk van Nydeggen at the Battle of Amerongen on 23 June 1585.