He was the eldest son of García Iñíguez and grandson of Íñigo Arista, the first king of Pamplona. Fortún was born at an unknown date, being the eldest son of García Iñíguez, king of Pamplona, and a woman named Urraca, which is believed to have been the granddaughter of Musa ibn Musa ibn Qasi, the leader of the Banu Qasi clan.
He appears in Arabic records as Fortoûn ibn Garsiya (فرتون بن غرسية). Reigning for about thirty years, Fortún Garcés would be the last king of the Íñiguez dynasty. Little is known about his early life.
King García Íñiguez had worked towards a closer relationship with the Kingdom of Asturias, distancing himself and his kingdom from the Banu Qasi dynasty that ruled the lands near the Ebro river.
The Wali of Zaragoza Muhammad ibn Lop sieged and ultimately destroyed the castle of Aibar, resulting in the death of the king García Íñiguez. After the death of his father, Fortún Garcés was allowed to return to Pamplona to take his place as king.
Fortún Garcés reigned with a policy very accommodating to the wishes of the Banu Qasi clan, which caused anger between the Pamplonese nobility. He would frequently retire to the Monastery of Leyre.
A drastic change took place in 905, when Sancho Garcés was chosen by the Pamplonese nobility to replace Fortún Garcés as king.
The reasons behind this decision reside in the fact that Sancho Garcés had a very well respected military prestige and had the support of important figures such as Raymond I, Count of Pallars and Ribagorza, Galindo Aznárez II, Count of Aragon and Alfonso III, King of Asturias. Besides, Sancho Garcés was related to the ruling monarchs, although part of a different dynasty, the House of Jiménez. Fortún Garcés permantently retired to the Monastery of Leyre in 905, where he died in 922.
