Educated as an attorney in Paris and admitted to the bar in 1887, he practiced briefly in Algeria, but returned to make his career in metropolitan France.
He became secretary to the Socialist deputy Alexandre Millerand, forming a lasting political and personal link. In 1893 Viviani himself entered the Chamber of Deputies.
By 1899 Viviani's doctrinaire views had cooled visibly. He was considered open to an invitation to join a bourgeois government an unheard of action for a Socialist up to that time but the offer went to the more experienced Millerand. Viviani was defeated in the election of 1902 and returned to the Chamber only in 1906. In the interim, he broke with the newly unified and militant French Socialist party, the SFIO, becoming one of a score of former Socialists to form a loose bloc of "Independents," to the right of the SFIO but to the left of the Radicals. Viviani joined the cabinet of Georges Clemenceau, then that of Aristide Briand, to serve as France's first minister of labor, 1906-1910.
By 1914 Viviani had established himself as one of France's most talented orators and as a flexible and moderate member of the parliamentary Left. Chosen to be premier by Raymond Poincare, he failed to get the necessary majority from the Radical-dominated Chamber of Deputies on his first try in early June 1914. After a brief interlude during which France had no Cabinet, Viviani received the Chamber's tepid approval. His skills notwithstanding, he had a reputation for both laziness and excitability. He lacked the administrative and political experience customarily offered by would-be premiers: he had been neither minister of finance nor minister of foreign affairs. He was probably chosen by Poincaré precisely because he could be swayed on crucial issues. A nominal member of the political Left open to Poincaré's ideas on three-year military service and the broader issues of a vigorous nationalist style in foreign affairs, Viviani constituted a valuable find.
On July 15, 1914, Viviani and Poincare left for a long-planned visit to St. Petersburg. Viviani found himself in a subordinate position as Poincare assumed control of the negotiations. On July 26, en route home by way of Scandinavia, the party received messages from Paris that made the gravity of the international situation clear. Viviani agreed to Poincaré's suggestion for an immediate return to France; he also sent a restrained note to the Russians pledging support in the interest of a general peace. The French ambassador to Russia, Maurice Paléologue, possibly under Poincaré's instructions, ignored the message. Throughout the crisis, Paléologue urged the Russians forward and concealed from Paris such events as the rapid progress of Russian mobilization.
Viviani turned to Poincaré repeatedly during the development of the July crisis. Crucial messages to the Russians and the British were drafted under Poincaré's direction. According to Albertini, during July 30 and July 31, Viviani and his colleagues accepted the strength of prowar feeling in Paris and gave up efforts to block the outbreak of hostilities. With a view to opinion in Britain, they pulled French troops back a short distance from the frontier. Germany was to have the opportunity and the onus of opening hostilities. Viviani's war message of August 4 to the National Assembly was accurate in its main lines; however, it ignored the crucial factor of Russia's general mobilization and France's contribution thereto as elements leading to war.
Indecisive and overly reliant on others in the prewar crisis, Viviani played the same role during the war. Strong pressure from Poincaré overcame the premier's objections and led in late August 1914 to the broadened union sacrée government. Viviani found himself helpless in the face of General Joffre's insistence on a free hand in running the war. He was reduced to complaining to the commander in chief about a lack of information concerning military operations before the battle of the Marne. By October Viviani found himself barred from touring the war zone on the deadlocked western front; he was being treated like any other member of the National Assembly. His old colleague Millerand, minister of war in the union sacrée government, became one of his principal burdens: a parliamentary spokesman for Joffre's quasi-dictatorship over the direction of the war.
In 1915 Viviani presided ineffectually over the bloody stalemate in the west: Joffre conducted fruitless major offensives in March and September. Unrest in the National Assembly grew. It centered on the immediate issue of visits to the front but soon encompassed the entire direction of the war. Ready to oust Millerand, Viviani gave in to Poincare's objection that such steps would fracture the union sacrée.
Viviani also contributed to the birth of France's commitment in the Balkans. He enthusiastically accepted Poincares suggestion (January 1915) that a Balkan front be opened. Joffre turned the idea down, but later that month Viviani took the first step toward Salonika. He accepted a British plan, seconded by his Navy Minister Victor Augagneur, that France join a maritime expedition to force the Dardanelles. When it failed in mid-March, France like Britain geared up for a larger effort. By midsummer Viviani's shaky government needed a victory somehow, somewhere. Meanwhile, the Radicals demanded a suitable post for their hero, General Maurice Sarrail, recently dismissed from his command in France by Joffre, and the course seemed set for a major French effort at the Dardanelles. Events merely moved the landing westward. Austro- German forces invaded Serbia from the north in early October; a Bulgarian assault on France's lone Balkan ally from the east followed within a week. The need for a rescue mission to bolster the Serbs led to an Anglo-French landing at Salonika.
The plunge into the Balkans came too late to save Viviani. Joffre's fall offensive in the Champagne had failed. Parliamentary commissions had voiced concern over Serbia's exposed position for months without catching Viviani's attention. Bulgaria's entry into the war on the enemy side brought the government down in late October. Pressed between the millstones of a restless National Assembly and a jealously self-contained High Command, Viviani had never been able to provide a clear direction for the war effort. He remained in the Cabinet, but his days at the center of power were over; he undertook missions to Russia in 1916 and the United States in early 1917.
In the postwar period Viviani represented France at the Washington Naval Conference of 1921 and at the Council of the League of Nations. He died outside Paris, September 6, 1925.
Viviani was drawn to socialism as a young man, making an early reputation for himself as a fiery anticlerical speaker and journalist. Much of his legal work he devoted to representing striking workers.