He was the son of Pribina and his Bavarian wife. He received a Bavarian name, Gozil, which was used in the Slavic form. He was probably born before or just after his father was expelled by Mojmír I, duke of the Moravians, because he went with his father to the Bulgarian Empire shortly afterwards. He also followed his father when he returned to East Francia where King Louis the German granted Pribina the parts of Pannonia around the Zala. In 850, Koceľ was present at the consecration of the church dedicated to the Blessed Virgin Mary in Blatnograd.
After the death of his father, probably in 861, Koceľ inherited his fiefs in Pannonia.
In 867, he hosted at his seat in Blatnograd (today: Zalavár, Hungary) the Byzantine brothers, Saints Cyril and Methodius when they were on their journey to Rome. They established a religious school in Blatnograd and educated around 50 students. Koceľ played an important role in the propagation of Christianity, when he asked Pope Adrian II to let Methodius return to him and the Pope fulfilled his request; later, he also asked the Pope to ordain Methodius to the See of Saint Andronicus. The arrival of Methodius gave rise to conflicts with the Archbishop of Salzburg whose Episcopal See Pannonia had traditionally belonged to.
The exact date and circumstances of his death are unknown.
In Slovak, his name is spelled Koceľ. In Slovenian, his name is spelled Kocelj. In Greek, his name is spelled Kotzeles. He is known from Bavarian and Papal documents as Chozil, Chezil, Chezul, Gozil.