Born on 11 November 1082 in Rodez, Viscounty of Rodez, County of Toulouse, Francia, he was the son of Ramon Berenguer II. He succeeded his father to co-rule with his uncle Berenguer Ramon II. He became the sole ruler in 1097, when Berenguer Ramon II was forced into exile.
Responding to increased raids into his lands by the Almoravids in 1102, Ramon counter-attacked, assisted by Ermengol V, Count of Urgell, but was defeated and Ermengol killed at the battle of Mollerussa.
During his rule Catalan interests were extended on both sides of the Pyrenees. By marriage or vassalage he incorporated into his realm almost all of the Catalan counties (except Urgell and
Peralada). He inherited the counties of Besalú (1111) and Cerdanya (1117) and in between married Douce, heiress of Provence (1112). His dominions then stretched as far east as Nice.
In alliance with the Count of Urgell, Ramon Berenguer conquered Barbastro and Balaguer. He also established relations with the Italian maritime republics of Pisa and Genoa, and in 1114 and 1115 attacked with Pisa the then-Muslim islands of Majorca and Ibiza. They became his tributaries and many Christian slaves there were recovered and set free. Ramon Berenguer also raided mainland Muslim dependencies with Pisa's help, such as Valencia, Lleida and Tortosa. In 1116, Ramon traveled to Rome to petition Pope Paschal II for a crusade to liberate Tarragona. By 1118 he had captured and rebuilt Tarragona, which became the metropolitan seat of the church in Catalonia (before that, Catalans had depended ecclesiastically on the archbishopric of Narbonne).
In 1127, Ramon Berenguer signed a commercial treaty with the Genoese. Toward the end of his life he became a Templar. He gave his five Catalan counties to his eldest son Ramon Berenguer IV and Provence to the younger son Berenguer Ramon.
He died on 23 January/19 July 1131 and was buried in the Santa Maria de Ripoll monastery.