Police, the coastguard and an MoD police launch were called to the discovery on Eastney beach.
A spokeswoman for the coastguard said they had been alerted by Hampshire police at 8.50am.
The beaches at Eastney and Hayling were cleared and a controlled explosion was conducted by the army’s explosive ordnance disposal team just after 11.40am.
Portsmouth police tweeted: ‘Not the usual start to the day after our shift dealt with an unexploded bomb down by the waterfront!
‘Nobody injured and big thanks to @BritishArmy and their explosive ordnance disposal team.’