O'Neill played Hugh in the smash-hit series, Sons of Anarchy. An autopsy is now pending.
TMZ, citing law enforcement sources, reported on June 8 that O'Neill's body was discovered by his girlfriend in the hallway of her Los Angeles apartment Wednesday night. O'Neill reportedly had a history of heart problems and a long-running smoking habit.
Reports have suggested no foul play is suspected, with an autopsy to be completed soon.More news: No chemo? Triangle doctors excited by new findings for breast cancer patients
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. Following Sons of Anarchy, O'Neill had a minor role in the 2016 film Urge, which starred Pierce Brosnan and Danny Masterson.
As reports of his death emerged tonight, shocked friends and fans took to social media to share fond memories of Alan.
Sons of Anarchy star Alan O'Neill has died at the age of 47, it has been confirmed.More news: Karnataka: Protests hinder screening of Rajinikanth’s film ‘Kaala’
Actress Kristen Renton added: "RIP sir... my you find peace now". Thank you for your kindness. "My thoughts are with his partner, children, family and friends at this time".
Fair City's Seamus Power, who plays Dermot on the show, said he "always enjoyed working with him".More news: NASA's Curiosity rover discovers organic matter on Mars