His loss of the electorate strengthened the Catholic Counter-Reformation in the northern German states, gave the Jesuits a stronghold in Cologne, and expanded the Wittelsbach family influence in imperial politics.

Gebhard was born in the Fürstenburg fortress of Heiligenberg, the second son of William, known as the younger, (6 March 1518 – 17 January 1566), Freiherr and Seneschal of Waldburg and an Imperial councilor, and his wife, Johanna v. Fürstenberg (1529–1589).

He received a broad, Humanist education, learned several languages, including Latin, Italian, French, and German, and studied history and theology.

His life at Augsburg caused some scandal; Uncle Otto, the archbishop, petitioned the Duke of Bavaria to remonstrate with Gebhard about his conduct, which apparently led to some improvement in his behavior.

[11] Gebhard is chiefly noted for his conversion to the reformed doctrines, and for his marriage with the reportedly beautiful Agnes von Mansfeld-Eisleben, a canoness of Gerresheim.

[15][14] The clause concerning ecclesiastical reservation in the religious Peace of Augsburg was interpreted in one way by his friends, and in another way by his foes; the former held that he could retain his office, the latter insisted that he resign.

[16] He placed the evangelical confession on parity with the Catholic one; furthermore, Gebhard adhered not to the teachings of Martin Luther, but to those of John Calvin, a form of religious observation not approved of in the Augsburg conventions of 1555.

[20] Ernst had the support of the previous Elector, now Salentin IX of Isenburg-Grenzau, Frederick, Duke of Saxe-Lauenburg, and, probably most important, several thousand Spanish troops hired by the pope.

[21] None of the combatants were prepared to commit their troops in a fixed battle; it was far more lucrative, and safer as well, to use them in a show of force, intimidating the peasantry, besieging walled towns and small cities, and limiting trade and the sale of food-stuffs in the marketplaces.

[22] By the end of March, Salentin, Frederick, and the few thousand Spanish troops drove Gebhard from Bonn, then from Bad Godesberg; he and his wife took refuge into Vest Recklinghausen, a fiefdom of the electorate.

There, he and Agnes encouraged a spurt of iconoclasm by their troops, alienating many heretofore supporters, including Hermann von Hatzfeld, seneschal of Balve.

[25] By 1588, Gebhard's joint pain (Gelenkenschmerz) prevented him from riding a horse; the climate of Cologne, damp and cold, made his condition worse, so he relinquished his claim on the Electorate to the protection of Adolf von Neuenahr and Martin Schenck, which they pursued until their deaths later that year.

Before his arrival some trouble had arisen in the chapter when three excommunicated canons, refugees from the Cologne strife, persisted in retaining their offices after they had accepted the reformed doctrines.

When Karl died on 18 June 1593, and was buried in the Strasbourg cathedral, Gebhard wrote a codicil leaving Agnes to the care and protection of the Duke of Württemberg.

"[33] Walter Goetz described him in less complimentary terms: he "was impelled by no great idea, nor could he claim through virile activity the title to any high striving ambition" and was "wanting in both depth and tenacity".

[34] Philip Motley described Gebhard thus: despite his swearing an oath to renounce his see if he should marry, "the love of Truchsess for Agnes Mansfeld had created disaster, not only for himself but for all of Germany."