Best known for his portrayal of Hugh in the cult motorbike gang crime drama, O'Neill also appeared in Irish soap Fair City and several films.
Sons of Anarchy star Alan O'Neill has died at the age of 47, it has been confirmed.
The Irish-born star, who appeared as Hugh in seasons six and seven of the hit series, was found unresponsive by his girlfriend at his Los Angeles apartment on Wednesday evening, according to TMZ. He was also apparently struggling with a drinking problem.
In a statement to Independent.ie, O'Neill's manager Greg Meyer said: "He was a great guy who was very amusing and engaging as well as a very talented actor".
Sons of Anarchy has lost a member of its crew.
An autopsy will be carried out but his death is not being treated as suspicious according to TMZ.
O'Neill's acting career dates back to the 1990s.
A great friend who taught me so much. The Kerri-Ann actress shared a number of photos of her with O'Neill on the set of the film, tweeting that he will be sadly missed, while sharing her thoughts and prayers with his family.
Entrepreneur Shawn Steiner posted: "Just heard my long time friend passed away this morning Alan O'Neil - RIP my friend". "May he rest in peace".