Born on June 14, 1993, in Newcastle upon Tyne, O’Neil began his professional career at West Bromwich Albion, where he spent several years coming up through the youth ranks before making his first-team debut in 2012. He also had loan spells at Scunthorpe United and Chesterfield during his time at West Brom. In 2015, O’Neil moved to Cambridge United, where he made over 100 appearances before joining Notts County in 2018. He then signed with Boreham Wood in 2021.