Rochambeau was born in Vendôme, in the province of Orléanais (now in the département of Loir-et-Cher). He was schooled at the Jesuit college in Blois. After the death of his elder brother, he entered a cavalry regiment, and served in Bohemia, Bavaria, and on the Rhine, during the War of the Austrian Succession. By 1747 he had attained the rank of colonel.
He took part in the siege of Maastricht in 1748 and became governor of Vendôme in 1749. After distinguishing himself in the Battle of Minorca (1756) on the outbreak of the Seven Years' War, he was promoted to Brigadier General of infantry. In 1758, he fought in Germany, notably in the battles of Krefeld and Clostercamp, receiving several wounds during the latter.
In 1780, Rochambeau was appointed commander of land forces as part of the project code named Expédition Particulière. He was given the rank of Lieutenant General in command of some 7,000 French troops and sent to join the Continental Army, under George Washington. In the American Revolutionary War Rochambeau commanded more troops than Washington did. Count Axel von Fersen the Younger served as Rochambeau's aide-de-camp and interpreter. The small size of the force at his disposal made him initially reluctant to lead the expedition.
He landed at Newport, Rhode Island, on 10 July, but was held there inactive for a year, due to his reluctance to abandon the French fleet blockaded by the British in Narragansett Bay. Brown University, then named the College in the Colony of Rhode Island and Providence Plantations, served as an encampment site for some of Rochambeau's troops, and the College Edifice, now known as University Hall, was converted into a military hospital. In July 1781, Rochambeau's force left Rhode Island, marching across Connecticut to join Washington on the Hudson River in Mount Kisco, New York. From July 6 to August 18, 1781, the Odell farm served as Rochambeau's headquarters. There then followed the celebrated march of the combined forces, the siege of Yorktown and the Battle of the Chesapeake. On 22 September, they combined with the Marquis de Lafayette's troops and forced Lord Cornwallis to surrender on 19 October. In recognition of his services, the Congress of the Confederation presented him with two cannons taken from the British. These guns, with which Rochambeau returned to Vendôme, were requisitioned in 1792.
He was an original member of The Society of the Cincinnati.