He worked for the Archbishop-Elector of Cologne and Louis XIV of France at the same time, and was arrested and tried for treason for convincing the Elector to fight on the opposite side of a war from the Empire.

[2] In 1648, Wilhelm was made subdeacon in the cathedral chapter at Cologne, and the following year joined Franz as a member of the Archbishop-Elector's privy council.

Wilhelm also reported this result in person to the Cardinal and Louis XIV, and let them know that the French king did not have a reasonable chance with the electors.

Wilhelm insisted on a document spelling out the benefits offered, as he was concerned the French might leave him out to dry after he showed himself too strongly opposed to the Habsburgs.

[6] On 4 June 1658, Lionne, Franz, and Wilhelm signed an agreement detailing French support for the counts should they continue to work "for all the plans and interests of His Majesty in Germany".

[8] In 1659, Cardinal Mazarin asked Maximilian and Johann Philipp von Schönborn, the Elector of Mainz, to oversee negotiations to end the Franco-Spanish War.

[9] In 1661, Wilhelm spent months in Paris conveying the suit of Charles IV, Duke of Lorraine, who wished to marry Anne Marie Louise d'Orléans, Duchess of Montpensier.

[13] When Philip IV of Spain died in 1665, the great powers wondered how long his heir, the sickly Charles II, would last.

He also visited the Count Palatine of Neuburg, Philip Wilhelm, and the Elector of Bavaria to persuade them not to allow Austrian forces to move through their lands to oppose French maneuvers in the Netherlands.

[14] On 8 January 1667, Wilhelm went to Vienna representing Cologne (but acting on behalf of France) to sound out the Emperor's feelings about the succession, perhaps splitting the Netherlands from Spain after the death of Charles.

[16] In early 1668, Wilhelm was negotiating with Grand Pensionary Johan de Witt to try to come to an arrangement in the War of Devolution to partition the Spanish Netherlands between France and the Dutch Republic.

That July, he had his brother, Hermann Egon, arrange a meeting so that it would appear the Dutch were negotiating trade agreements with the League of the Rhine against France.

[13] In 1670, while attempting to get Brandenburg to join the French alliance in the Franco-Dutch War, Wilhelm also asked the elector about his opinion of a successor for Leopold I, who was sick at the time.

[21] In 1672 the Emperor joined the Franco-Dutch War as an ally of the Dutch, finding himself opposed by several bishops in the northwest part of the Empire.

[22] The Fürstenberg brothers being regarded by the Imperialists as the main cause of this disaster, Wilhelm was arrested for treason on 14 February 1674 by imperial cavalry after chasing his carriage through Cologne.

As the progress of the Allies against Louis XIV in the Nine Years War deprived him of all prospect of success, Wilhelm Egon retired to France.