Born in 1763 in Vienna, Józef Poniatowski was the son of a Polish nobleman who had served as an artillery officer in the Austrian army and had been made Austrian ambassador to Poland. After the death of his father, Józef followed in his father's footsteps by enrolling in the Austrian army in 1780 with the rank of second-lieutenant. His advance was to prove rapid; in September 1784 he was promoted to major, and after a short interruption to his military career due to a broken leg, he became a colonel in the Austrian emperor's light cavalry. As ADC to Joseph II, Holy Roman Emperor and emperor of Austria, he participated in the Battle of Šabac in 1788 during the Austro-Turkish War (1787-1791) but was wounded. Soon after his recovery, he was summoned by his uncle, Stanisław August Poniatowski, king of Poland, and entered the newly-reorganised Polish army with the rank of major-general.
Following Polish constitutional reform introduced in 1791, Russian troops invaded Poland: Poniatowski was dispatched to Ukraine in command of 20,000 Polish troops with orders to resist the invading force. Despite success at the Battle of Zieleńce, Poniatowski was ordered to agree an armistice with the Russians; refusing, Catherine the Great insisted on surrender, which the Polish king eventually agreed to. Resigning his commission, Poniatowski returned to Vienna but his stay was to prove brief. Under pressure from Russia, the Austrian authorities hurried him along, and he eventually arrived in Brussels. During his exile, a Polish independent movement, led by Kościuszko, rose up and Poniatowski returned to Poland: this insurrection was crushed by the Russians – allied with Austria and Prussia – and Poland was broken up further. Refusing to enter Russian service, Poniatowski again left for Vienna but was obliged to travel to St. Petersburg in 1798 for the funeral of his uncle, who had abdicated his throne and lived out his remaining years in the Russian capital. Returning to Warsaw, he set up home in Pod Blacha palace in the company of his mistress, the Countess de Vaubin: following a period of financial difficulty, he was made military governor of Warsaw by the king of Prussia, Friedrich Wilhelm III, with orders to organise the national guard and defend the city against the invading French forces. The defence was short-lived and following Napoleon's arrival in Warsaw in December 1806, Poniatowski presented Napoleon with a note calling for a Polish state.
In the provisional government set up by Napoleon in the Polish provinces, Poniatowski was made Minister of War, a role which he fulfilled to the satisfaction of the French authorities. In 1807, Poniatowski became Minister of War and commander-in-chief of the army for the newly-created Duchy of Warsaw. In exchange for French financial assistance in constructing defence works and expanding the Polish army, Poniatowski was obliged to contribute troops to the defence of Danzig, Pomerania and Silesia, as well as Napoleon's campaign in Spain (where Polish lancers fought in the Battle of Somosierra). With the Duchy left drastically short of armed forces, the Franco-Austrian war of 1809 saw Poniatowski surprised by Archduke Ferdinand, who invaded the duchy at the head of 30,000 soldiers. Leading the defence at Raszyn, Poniatowski was forced to accept the futility of his resistance and returned to Warsaw to announce the imminent arrival of the Austrians. Blamed for the defeat, he nevertheless agreed a favourable withdrawal from the capital and proceeded to Galicia, where he mounted a counteroffensive and raised up an insurrection, forcing the Austrians to evacuate Warsaw. Following Napoleon's success at Wagram, Poniatowski proceeded immediately to Krakow – the historic capital of Poland – where he kept a close eye on peace negotiations between a defeated Austria and France. The majority of the territory ceded by Austria – including Krakow and Lublin – was incorporated into the Duchy of Warsaw and Poniatowski's role in events was recognised by Napoleon, who made him Grand-officier of the Légion d'honneur.
As Franco-Russian relations began to break down, two camps began to form in Warsaw: one – under the leadership of Prince Czartoryski – convinced that Polish national interests lay with Russia and Alexander I, and the other – headed by Poniatowski – insistent on remaining close to Napoleon. With Alexander organising troops along the Russian-Polish border, Poniatowski took the opportunity presented by the Roi de Rome's baptism in June 1811 to present in person his concerns to Napoleon. Napoleon's subsequent invasion of Russia saw Poniatowski take command of the Polish troops in the Grande Armée's fifth corps, under the command of Jerome Bonaparte. Following Jerome's departure from the army, Poniatowski took command of the entire right-wing of the army. He led his troops ably at Smolensk and at the Battle of Borodino, but his losses were huge. Although he entered Moscow on 14 September, the Grande Armée's stay was to prove brief. On 19 October, Napoleon ordered the retreat and Poniatowski's troops formed the rear-guard of the departing army. During the passage through Viazma, his horse slipped on some ice and Poniatowski, injured, was forced to hand over command to a subordinate, General Zayonchek. The remnants of the fifth corps reached Warsaw on 13 December, where they remained until February 1813. With the Russian army about to enter Warsaw, Poniatowski set out on 5 February with orders to fall back on Krakow. Refusing Alexander's offers to join his cause, Poniatowski organised 14,000 troops and departed for Saxony with the intent of joining up with Napoleon. He reached Napoleon in Dresden, and Poniatowski's troops became the eighth corps of the Grande Armée. On 16 October, 1813, during the Battle of Leipzig, Napoleon made Poniatowski Maréchal de France in recognition of his loyal service. After three days of intense fighting, Napoleon gave the order to withdraw across the Elster and destroy the bridges once his troops had successfully made it across; Poniatowski's Polish troops were given the task of defending the retreat. On 19 October, an engineer mistakenly destroyed the bridges before the Polish troops had completed their retreat: wounded in a number of places, Poniatowski was shot in the chest whilst scaling the south bank of the Elster and was drowned. His body was recovered, embalmed, and transported to Warsaw. He was shortly afterwards laid to rest in Krakow cathedral alongside the kings of Poland.