Raymond IV is sometimes known as Raymond of Saint-Gilles, after the family seat to the south of Nīmes. He was Count of Toulouse, Marquis (or Margrave) of Provence, and one of the leaders of the First Crusade. He succeeded his brother William IV as Count of Toulouse in 1088.

According to an Armenian source, he had lost an eye on a pilgrimage to Jerusalem before the First Crusade. He fought against the Moors in Spain before 1096, and he was the first to join the crusade after Pope Urban II's sermon at the Council of Clermont.

Raymond IV was the senior nobleman among the five leaders of the First Crusade. The oldest and the richest of the crusaders, Raymond IV left Toulouse at the end of October 1096, with a large company that included his wife Elvira, his son Bertrand, and Adhemar, bishop of Puy, the papal legate. He marched to Dyrrhachium, and then east to Constantinople along the same route used by Bohemund of Taranto. At the end of April, 1097, he was the only crusade leader not to swear an oath of fealty to Byzantine Emperor Alexius I - instead he swore an oath of friendship, and offered his support against Bohemund, both Raymond and Alexius' mutual enemy. (Consequently, he was the only western Crusader not to break his solemn oath). He was present at the siege of Nicaea and the Battle of Dorylaeum in 1097, but his first major role came in October of 1097 at the siege of Antioch. The crusaders heard a rumour that Antioch had been deserted by the Seljuk Turks, so Raymond sent his army ahead to occupy it, offending Bohemund of Taranto who wanted the city for himself. The city was, however, still occupied, and was taken by the crusaders only after a difficult siege in June of 1098. Raymond took the palatium cassiani (the palace of the emir, Yaghi-Siyan) and the tower over the Bridge Gate. He was ill during the second siege of Antioch by Kerbogha, and so missed an outbreak of bogus miracles, which culminated in the discovery of the Holy Lance by a monk named Peter Bartholomew.

Adhemar of Le Puy (in red) acclaims Raymond IV (in white and gold) as leader of the First Crusade, according to a nineteenth century French artist.

The "miracle" raised the morale of the crusaders, and to their own surprise they were able to rout Kerbogha outside Antioch. The Lance itself became a valuable relic among Raymond's followers, despite Adhemar of Le Puy's skepticism and Bohemund's outright mockery. Raymond refused to give up his territories in the city to Bohemund, reminding him that he should return to the city to Emperor Alexius, as he had sworn to do. A struggle then arose between Raymond's supporters and the supporters of Bohemund, partly over the genuineness of the Lance, but also over the possession of Antioch.

Many of the minor knights and foot soldiers preferred to continue their march to Jerusalem, and they convinced Raymond to lead them there in the autumn of 1098. Raymond IV led them out to besiege Ma'arrat al-Numan, although he left a small detachment of his troops in Antioch, where Bohemund also remained. As Adhemar had died in Antioch, Raymond, along with the prestige given to him by the Holy Lance, became the de facto leader of the crusade, but Bohemund expelled his detachment from Antioch in January of 1099. Raymond then began to search for a city of his own. He marched from Ma'arrat, which had been captured in December of 1098, into the emirate of Tripoli, and began the siege of Arqa on February 14, 1099, apparently with the intent of founding an independent territory in Tripoli that could limit the power of Bohemund and contain the Principality of Antioch to the south.

The siege of Arqa, a town outside Tripoli, held out longer than Raymond had hoped. Although he captured Hisn al-Akrad, a fortress that would later become the important Krak des Chevaliers, his insistence on taking Tripoli delayed the march to Jerusalem, and he lost much of the support he had gained after Antioch. Raymond finally agreed to continue the march to Jerusalem on May 13 and, after months of siege, the city was captured on July 15. Raymondwas offered the crown of the new Kingdom of Jerusalem, but refused, as he was reluctant to rule in the city in which Jesus had suffered. It is also possible that he preferred to continue the siege of Tripoli rather than remain in Jerusalem. He was also reluctant to give up the Tower of David in Jerusalem, which he had taken after the fall of the city, and it was only with difficulty that Godfrey of Bouillon was able to take it from him.

Raymond participated in the battle of Ascalon soon after the capture of Jerusalem, during which an invading army from Egypt was defeated. However, Raymond wanted to occupy Ascalon himself rather than give it to Godfrey, and in the resulting dispute Ascalon remained unoccupied. It was not taken by the crusaders until 1153. Godfrey also blamed him for the failure of his army to capture Arsuf. When Raymond went north, in the winter of 1099-1100, his first act was one of hostility against Bohemund, capturing Laodicea from Bohemund (who had himself recently taken it from Alexius). From Laodicea he went to Constantinople, where he allied with Alexius I, Bohemund's most powerful enemy. Bohemund was at the time attempting to expand Antioch into Byzantine territory, and once again refused to fulfill his oath to the Byzantine Empire.

Raymond IV joined the minor and ultimately unsuccessful crusade of 1101, which was defeated at Heraclea in Anatolia. He escaped and returned to Constantinople. In 1102 he travelled by sea from Constantinople to Antioch, where he was imprisoned by Tancred, regent of Antioch during the captivity of Bohemund, and was dismissed only after promising not to attempt any conquests in the country between Antioch and Acre. He immediately broke his promise, attacking and capturing Tortosa, and began to build a castle on the Mons Peregrinus ("Pilgrim's Mountain") which would help in his siege of Tripoli. He was aided by Alexius I, who understanably preferred a friendly state in Tripoli to balance the hostile state in Antioch.

Raymond died in 1105, before Tripoli was captured. He was succeeded by his nephew William-Jordan, who, in 1109, with the aid of King Baldwin I of Jerusalem, finally captured the town and established the County of Tripoli.William was deposed in the same year by Raymond's eldest son Bertrand, and the county remained in the possession of the counts of Toulouse throughout the 12th century.

Raymond IV of Toulouse seems to have driven both by religious and material motives. On the one hand he accepted the discovery of the Holy Lance and rejected the kingship of Jerusalem, but on the other hand he could not resist new territory. Raymond of Aguilers, a clerk in Raymond IV's army, wrote an account of the crusade from Raymond's point of view.

The Counties of Toulouse and Tripoli were inherited by Bertrand, but on his death the County of Toulouse reverted to his brother Alphonse-Jordan, while the County of Tripoli went to Pons, Bertrand's son. The dynasty of the Counts of Tripoli continued over several generations until the Crusaders were definitively defeated by Saladin at the Horns of Hattin.