Police officers were called to reports a 23-year-old man had collapsed at a Beastfair nightclub - which the Express understands is Big Fellas - at around 12.15am this morning.
He was taken to hospital but was pronounced dead on arrival.
Police are investigating, but say they are not treating his death as suspicious.
In a separate incident at around 10pm on Saturday, police were called to reports of a disturbance involving a "number of people" on Cornmarket in the town.
A West Yorkshire Police spokesman said one man was arrested on suspicion of assault and is currently in police custody.
Keep checking the Express website for updates.