According to his Vita, written by Braulius, bishop of Caesaragusta (modern Zaragoza) roughly a hundred years after Aemilian's death, the saint was a shepherd until a sudden conversion, perhaps around the age of twenty, decided him upon the eremitical life. He sought out a more experienced hermit in Bilibio, Felix (although known more usually by the Spanish form of his name, San Felices), where he lived for a number of years. He then left his master, and lived as a hermit (perhaps even a gyrovagus) in the mountains, whence he was summoned and ordained as priest in Berceo by Didymus the Bishop of Tarazona.
In order to escape the duties of the clerical life, he distributed the monies of the church to the poor to such an extent that he aroused the opposition of his fellow priests and was allowed to return to the wilderness.
There he lived attracting a large following amongst the laity and a small community of disciples around his cell. He died at a venerable age, and was buried in his cell. Some few miracles are recorded by Braulius as having occurred after Aemilian's death.
He is a patron saint of Spain, where he is known as San Millan de la Cogolla, the cowled Saint Emilian.
Gonzalo de Berceo wrote an account of his life called the Vida de San Millán de la Cogolla.