Police said they were called to reports of two men being punched at the Ricco and Loren bar on Market Street, Lichfield, at 23:25 BST on Sunday.
Officers said one of the men, O’Gara, died in hospital on Tuesday afternoon, while the second, who also went to hospital, was discharged.
Allison, 36, from Solihull, is accused of murdering O’ Gara and causing grievous bodily harm in relation to the latter.
He was remanded in custody and is next due to appear at Stafford Crown Court on 1 September.