This section contains spoilers for: Dragon Age: Redemption.
Prior to the events described in the series, he was a DalishKeeper for Josmael's clan. His clan was responsible for guarding an artifact called the Mask of Fen'Harel. He was captured by templars and taken to a Chantry prison. In there, he was being interrogated, likely about the artifact. In prison he also met Saarebas, who managed to learn Yevven's knowledge of the Mask through magic.
According to Cairn, Yevven died, though it was not shown on screen.