Emergency services, including police, ambulance and coastguard, were called to the harbour on Saturday night.
The 56-year-old man was pulled out of the water and rushed to Aberdeen Royal Infirmary, but was pronounced dead a short while after arrival.
A police spokesman said: “Around 10.35pm on Saturday, January 22, officers were called to Peterhead Harbour.
"A 56-year-old man was recovered from the water and taken to Aberdeen Royal Infirmary where he was pronounced dead a short time later.
“There are no suspicious circumstances surrounding the death and a report will be forwarded to the procurator fiscal.”