He came of a bourgeois family in Lorraine, and was born at Bar-le-duc. He soon decided on a military career, and served in the regiment of Medoc from 1784 to 1787, when, having no hope of promotion on account of his non-noble birth, he retired with the rank of sergeant. The French Revolution changed his fortunes, and in 1792, on the outbreak of war, he was elected lieutenant-colonel of the 3rd battalion of the volunteers of the Meuse. His gallant defence of the little fort of Bitsch in the Vosges in 1792 drew attention to him; he was transferred to the regular army in November 1793, and after serving in numerous actions on the Belgian frontier he was promoted general of brigade in June 1794 for his conduct at the Battle of Kaiserslautern.
He continued to serve with distinction on the German frontier under Hoche, Pichegru and Moreau, and was repeatedly wounded and once (in 1795) taken prisoner. He was Andre Massena's right hand all through the great Swiss campaign of 1799--first as a general of division, and then as chief of the staff--and won extraordinary distinction at the Battle of Zürich. He was present under Massena at the defence of Genoa, and so distinguished himself at the Battle of Monzambano that Napoleon presented him with a sword of honour. He was made inspector-general of infantry, and, on the establishment of the empire, given the Grand Cross of the Legion of Honour, but was not included in the first creation of marshals.
He was, however, elected a member of the chamber of deputies, but had little time to devote to politics. He took a leading role in the war of 1805, commanding the famous division of "grenadiers Oudinot," made up of hand-picked troops and organized by him, with which he seized the Vienna bridges, received a wound at Hollabrünn, and delivered the decisive blow at Austerlitz. In 1806 he won the Battle of Ostrolenka, and fought with resolution and success at the Battle of Friedland. In 1808 he was made governor of Erfurt and count of the Empire, and in 1809, after displaying brilliant courage at Wagram, he was promoted to the rank of marshal. He was made duke of Reggio, and received a large money grant in April 1810. Oudinot administered the government of the Kingdom of Holland from 1810 to 1812, and commanded the II corps of the Grande Armée in the Russian campaign. He was present at Lützen and Bautzen, and when holding the independent command of the corps directed to take Berlin was defeated at Gross Beeren. He was then superseded by Marshal Ney, but the latter was defeated at the Battle of Dennewitz.
Oudinot was not disgraced. He held important commands at Leipzig and in the campaign of 1814. On Napoleon's abdication, he rallied to the new government, and was made a peer by King Louis XVIII. Unlike many of his old comrades, he did not desert to his former master in 1815. His last active service was in the French invasion of Spain in 1823, in which he commanded a corps and was for a time governor of Madrid. He died as governor of Les Invalides. Oudinot was not, and made no pretence of being, a great commander, but he was a great general of division. He was the beau-ideal of an infantry general, energetic, conversant with detail, and in battle as resolute and skilful as any of Napoleon's marshals.