South Yorkshire Police in northern England said it responded to reports at around 1:30 pm (1230 GMT) of a man entering the enclosure at the Yorkshire Wildlife Park, near the city of Doncaster.
“The tiger subsequently attacked the man, resulting in serious injury,” the force said in a statement.
“Emergency services attended and sadly, despite the vest efforts of medical personnel, the man was pronounced dead at the scene,” it added.
Police said earlier the tiger remained in the enclosure following the incident and that there was no wider risk to the public. All visitors had been evacuated.
The wildlife park confirmed that a “serious incident” had taken place at its tiger enclosure, triggering the closure of the attraction.
Yorkshire Ambulance Service said it had sent two ambulances by road and an air ambulance to the scene.
The park’s “Land of the Tigers” feature has a 300-metre (980-ft) raised walkway.
From the walkway, visitors can view the park’s Amur tigers in their enclosure which includes woodland, grassland and a waterfall pool.
There are estimated to be only around 500 of the endangered subspecies left in the wild.
The park is due to remain closed on Sunday.