The man is understood to have died within hours of the Euro 2016 match between Northern Ireland and Poland.
A local official said the man died after climbing a sea-front railing and falling onto a stony beach.
A police spokesman said: "Investigators suspect an accidental death."
His name has not been released.
Northern Ireland fan dies in Nice
13 June 2016
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A 24-year-old Northern Ireland soccer fan has died in Nice, French police have confirmed.
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