She spent most of her career assigned to the Mediterranean Squadron (escadre de la Méditerranée) and usually was chosen to serve as a flagship.

Saint Louis was ordered to the Dardanelles in November 1914 to guard against a sortie into the Mediterranean by the German battlecruiser SMS Goeben.

Saint Louis was transferred to the squadron assigned to prevent any interference by the Greeks with Allied operations on the Salonica front in May 1916, after a lengthy refit in France.

She carried a maximum of 1,050 tonnes (1,030 long tons) of coal which allowed her to steam for 4,200 miles (3,600 nmi) at a speed of 10 knots (19 km/h; 12 mph).

[1] Saint Louis carried her main armament of four 40-calibre Canon de 305 mm Modèle 1893 guns in two twin-gun turrets, one each fore and aft.

The ship's anti-torpedo boat defences consisted of twenty 40-calibre Canon de 47 mm Modèle 1885 Hotchkiss guns, fitted in platforms on both masts, on the superstructure, and in casemates in the hull.

Even before Saint Louis was formally commissioned, she participated in a naval review conducted by the President of France, Émile Loubet, at Cherbourg in July 1900.

[2] The following year, Saint Louis and the Mediterranean Squadron participated in an international naval review by President Loubet in Toulon with ships from Spain, Italy and Russia.

The ship was briefly transferred to the Northern Squadron (escadre du Nord), where she became its flagship, in October 1910,[2] and she participated in a large naval review by President Armand Fallières off Cap Brun on 4 September 1911.

[2] Together with the older French pre-dreadnoughts, the ship's first mission in the war was to escort troop convoys from North Africa to France.

Upon its completion, Saint Louis was ordered to the Eastern Mediterranean where she became the flagship of the newly formed Syrian Squadron (escadre de Syrie) on 9 February.

These ships were intended to attack Turkish positions and lines of communication in Syria, Lebanon, Palestine and the Sinai Peninsula.

Saint Louis participated in the bombardment of Gaza and El Arish in April before she was transferred back to the Dardanelles in May.

When the refit was completed in May 1916, Saint Louis was ordered to Salonica where she joined the French squadron assigned to prevent any interference by the Greeks with Allied operations in Greece where she arrived on 22 May.