A third male was arrested after police were called to a fight near the carnival ride section about 8pm tonight.
Police said they found two males suffering stab wounds and gave first aid before paramedics arrived.
They said both suspected victims were taken to Westmead Hospital, and one was in a critical condition, before later confirming one of the youths had died.
NSW Ambulance Inspector Mark Whittaker said when paramedics arrived the youth was in cardiac arrest having suffered a traumatic chest wound.
“Paramedics performed CPR and a number of other critical interventions at the scene before loading the patient for transport to Westmead Hospital, unfortunately despite best efforts he couldn’t be resuscitated,” he said, in a statement.
“There’s no doubt this would have been a very confronting scene for the dozens of witnesses who were out to enjoy an evening at the Royal Easter Show.”
Showgoers were moved out of the area and the crime scene was established.
Videos of the moments leading up to and following the incident have been shared extensively on social media.