Kosciuszko's family was an impoverished member of the minor nobility, and while they escaped the serfdom that constrained so much of the Commonwealth, Tadeusz needed to find a career. He attended school in Lubieszow and then the Cadet Academy in Warsaw before continuing his engineering studies in Paris, France.

Kosciuszko returned to Poland in 1774, but he remained there for less than two years. While many narratives hurry past this homecoming, highlighting Kosciuszko's undoubted desire to fight in the American struggle for independence, it is important to remember that several factors pushed the young captain away from Poland. In 1772 Prussia, Austria and Russia had partitioned Poland, seizing around 30% of its territory and forcing governmental changes through bribes, threats and arrests. There was no place in the Polish Army for Kosciuszko, and he began to tutor Ludwika Sosnowski, the daughter of a General. Some sort of affair followed, possibly involving a failed attempt to elope, and Tadeusz was forced to leave in 1775. He fled to France where, at some point in late 1775 or the first half of 1776, he heard about the American rebellion against the British. Kosciuszko left during the summer of 1776, perhaps in response to the colonist’s declaration of independence, and by the 18th of October he was a colonel in the Continental Army.

He was the first of a galaxy of foreign officers to receive a commission from the Continental Congress to serve in General Washington's army. Kosciuszko's skill as an engineer in charge of fortifications was instrumental in earning him the rank of brigadier bestowed upon him by congress in 1783.

Shortly after arriving in Philadelphia in 1776, Kosciuszko read the Declaration of Independence and was moved to tears because he discovered in this single, concise document everything in which he truly believed. When he discovered that Thomas Jefferson was responsible for drafting the Declaration, he felt compelled to meet him. A few months later, while moving south with the Continental Army, Kosciuszko stopped in Virginia to meet with Jefferson. After a very warm reception, the two men spent the day comparing philosophies and eventually became the best of friends.

In the early days of the war, Kosciuszko helped to fortify the Philadelphia waterfront at Fort Mercer. Shortly after, he was transferred to New York, where he helped with fortifications along the Hudson and planned the defense for Saratoga. The Battle of Saratoga became known as one of military history's most famous struggles for independence and proved to be a turning point in the war.

In 1778, Kosciuszko was made chief engineer of West Point, New York. This fortification became known as the American Gibraltar because it was unable to be penetrated by the British Army. Eventually West Point became a military academy, as suggested by Kosciuszko to General George Washington.

In 1783, Kosciuszko was appointed Brigadier General and was awarded the Cincinnati Order Medal by General George Washington, Commander-in-Chief of the Continental Army. Washington also presented Kosciuszko with two pistols and a sword as gifts for his outstanding service to America.

In 1784 Kosciuszko returned to his homeland and as an outstanding strategist, he commanded his troops during numerous battles in the war with Russia. Kosciuszko helped organize the Polish Army, and led his country to an adoption of a new constitution, consequently into an armed uprising against the two big powers Prussia and Russia. On March 24th Kosciuszko took his oath in Krakow: "I swear to the whole Polish nation that I shall not use the power vested in me for private oppression but that I shall exercise this power only in the defense of the whole of the frontiers and to regain the independence of the Nation and to establish universal freedom". After several victorious battles in October, 1794, the Polish forces suffered a defeat at Maciejowice. The commander, heavily wounded in the field, was taken prisoner. Kosciuszko remained in Russia as a prisoner until 1796 and was released on the condition he would never return to Poland.

Kosciuszko spent the last years of his life in Switzerland, where on October 15, 1817 he died at the age of 72. He is buried in Wawel Castle, in Krakow, Poland, among the tombs of the Polish Kings.