After the outbreak of World War I, Waldeck-Rousseau joined the main French fleet that blockaded the southern end of the Adriatic to prevent the Austro-Hungarian Navy from operating in the Mediterranean.

She thereafter alternated between stints in the southern Adriatic and patrols in the eastern Mediterranean once the Ottoman Empire joined the war in November.

The two Edgar Quinet-class cruisers proved to be the last major warship of the French fleet to rely on reciprocating machinery for their propulsion systems.

While on her acceptance trials on 2 February, she struck a submerged object that bent her port propeller shaft and damaged the screw.

[11] At the outbreak of World War I in August 1914, Waldeck-Rousseau was under repair at Toulon owing to a grounding incident off Golfe-Juan during a hurricane on 22 February.

[20] By the beginning of 1916, the fleet's modern armored cruisers had been organized into two units, the 1st and 2nd Light Divisions; Waldeck-Rousseau served in the former, which also included Edgar Quinet and Ernest Renan.

[21] On 8 January 1916, Waldeck-Rousseau, her sister Edgar Quinet, Ernest Renan and Jules Ferry embarked a contingent of Chasseurs Alpins (mountain troops) to seize the Greek island of Corfu.

The cruisers sent the troops ashore on the night of 10 January; the Greek officials on the island protested the move but offered no resistance.

[23] Starting in 1919, the French Navy joined the Allied intervention in the Russian Civil War in the Black Sea to support the Whites against the Red Bolsheviks.

While in Odessa on 26–29 April 1919, sailors aboard Waldeck-Rousseau mutinied; the ship, which had just arrived from France with a fresh crew, had not yet had contact with Russian revolutionaries.

[26] On 26 March 1920, Waldeck-Rousseau provided gunfire support to the evacuating White Russian forces outside Novorossiysk, along with the British dreadnought battleship Emperor of India.

[23] The motley collection of ships departed the Crimea on 14 November; Waldeck-Rousseau steamed at the rear of the fleet as it made its way to Constantinople.

The United States destroyer USS Bainbridge arrived on the scene first and took off the survivors, which numbered 482 of the 495 crew and passengers that had been aboard.

[31] She left France on 10 May and arrived on 22 June, where she replaced the cruiser Jules Michelet as the flagship of the French Far East Squadron.

After the Germans defeated France and occupied Brest, they prevented the French from returning aboard Waldeck-Rousseau; the vessel was slowly taking on water, and without the ability of the crew to operate her pumps, she eventually foundered on 8 August.

[33] During this period, in early 1942, the Germans raised the wreck and disguised Waldeck-Rousseau as the heavy cruiser Prinz Eugen as a decoy before they launched Operation Cerberus.