Born at Châtillon - sur - Loing in 1519, Gaspard came to court at the age of 22 and began a friendship with François of Guise. In the campaign of 1543 Coligny distinguished himself, and was wounded at the sieges of Montmédy and Bains. In 1544 he served in the Italian campaign under the Count of Enghien, and was knighted on the Field of Ceresole. Returning to France, he took part in different military operations; and having been made colonel general of the infantry (April 1547), exhibited great capacity and intelligence as a military reformer.

That year he married Charlotte de Laval (d. 1568). He was made admiral on the death of Claude d'Annebaut (1552). In 1557 he was entrusted with the defense of Saint - Quentin. In the siege he displayed great courage, resolution, and strength of character; but the place was taken, and he was imprisoned in the stronghold of L'Ecluse. On payment of a ransom of 50,000 crowns he recovered his liberty.

By this time he had become a Huguenot, through the influence of his brother, d'Andelot. The first known letter which John Calvin addressed to him is dated 4 September 1558.

Gaspard de Coligny secretly focused on protecting his co-religionists, by attempting to establish colonies abroad in which Huguenots could find a refuge. He organized the expedition of a colony of Huguenots to Brazil, under the leadership of his friend and navy colleague, Vice Admiral Nicolas Durand de Villegaignon, who established the colony of France Antarctique in Rio de Janeiro, in 1555. They were afterwards expelled by the Portuguese, in 1567.

Coligny also was the leading patron for the failed French colony of Fort Caroline in Spanish Florida led by Jean Ribault in 1562.

In 1566 and 1570, Francisque and André d'Albaigne submitted to Coligny projects for establishing relations with the Austral lands. Although he gave favorable consideration to these initiatives, they came to naught when Coligny was killed in 1572 during the St. Bartholomew's Day massacres.

Following the death of Henry II he placed himself with Louis, Prince of Condé, at the forefront of the Huguenot party, and demanded religious toleration and certain other reforms. In 1560, at the Assembly of Notables at Fontainebleau, the hostility between Coligny and François of Guise broke forth violently. When the civil wars began in 1562, Coligny decided to take arms only after long hesitation, and remained always ready to negotiate. In none of these wars did he show superior genius, but he acted throughout with great prudence and extraordinary tenacity; he was "le héros de la mauvaise fortune" ("hero of misfortune")

In the "first war" of 1562 - 63 he commanded the cavalry at the Battle of Dreux, the first major engagement and, unlike both commanders in chief, managed to avoid being captured, and withdrew in good order from the defeat. He was blamed by the Guise faction for the assassination of Francis, Duke of Guise at Orléans in 1563.

In the "third war" of 1569 the defeat and death of the Prince of Condé at the Battle of Jarnac left Coligny the sole leader of the Protestant armies. Victorious at the Battle of La Roche - l'Abeille, but defeated in the Battle of Moncontour on October 3rd, he entered into the negotiations for what became the Peace of Saint - Germain (1570). Marrying Jacqueline de Montbel, Countess d'Entremont, and returning to court in 1571, he grew rapidly in favor with Charles IX, becoming a close mentor to the weak, easily manipulated King.

As a means of emancipating the king from the tutelage of his mother and the faction of the Guises, the admiral proposed to him a descent on Spanish Flanders, with an army drawn from both faiths and commanded by Charles in person. The king's regard for the admiral and the increasingly bold demands of the Huguenots alarmed Catherine de' Medici, the Queen Mother.
The wedding of the Protestant Henry, King of Navarre, and Marguerite de Valois, the King's sister brought a great number of Huguenot notables to Paris, and political and religious tensions were running extremely high. On 22 August 1572, the day after the end of the wedding festivities, Coligny was shot in the street by a man called Maurevert from a house belonging to de Guise. However, the bullets only tore a finger from his right hand and shattered his left elbow. The would-be assassin escaped.

It never became clear who, if anyone, had hired or encouraged Maurevert to carry out the attempt but historians generally focus on three possibilities: the Guise family, Catherine de Medici, or the duke of Alba on behalf of Philip II of Spain. The King sent his own physician to treat Coligny and even visited him, but the queen mother prevented all private discourse between them.

The Catholics now feared Huguenot retaliation for the attempt on Coligny's life, and it was decided to pre-emptively assassinate their leadership, in what became known as the St. Bartholomew's Day massacre. As one of the main targets, on the night of 24 August, Coligny was attacked in his lodgings by a group led by Guise. After several of his entourage had been killed, a servant of the new Duke of Guise, Charles Danowitz or Jean Charles D´Ianowitz (Karel z Janovic), generally known as Besme or Bême (Noble Family from Bohemia (CZ) Janovský z Janovic), plunged a sword through Coligny's breast and threw his body out of a window to his master's feet. Coligny finally died when another of Guise's associates chopped off his head.

Historian Barbara B. Diefendorf, Professor of History at Boston University, wrote that Simon Vigor had "said if the King ordered the Admiral (Coligny) killed, 'it would be wicked not to kill him'. With these words, the most popular preacher in Paris legitimised in advance the events of St. Bartholomew's Day".

Coligny's papers were seized and burned by the queen mother; among them, according to Brantôme, was a history of the civil war, "very fair and well written, and worthy of publication".

By his first wife, Charlotte de Laval (1530 - 1568), Gaspard had three children. By his second wife, Jacqueline de Montbel (1541 - 1588), the Countess d'Entremont and Launay-Gelin, Gaspard had one daughter, Beatrice, who became Beatrice de Coligny (b. 1572), Countess d'Entremont.