The 7ft explosive, which dated back to the Second World War, was dredged up by a fishing vessel near Needles at about 8am on Saturday.
Divers placed the device, which contained 2,000lb of explosive, back on the seabed before bomb disposal experts blew it up shortly before 11am on Sunday.
HM Naval Base Portsmouth tweeted: “Our bomb disposal experts safely destroyed a 2,000lb German sea mine this morning near the Needles.
“Dredged up yesterday by a fishing vessel the divers placed it back on the seabed and started #Sunday with a #BOOM Our #heroes for keeping our waters safe.”
Piers Stanbury, of the coastguard agency, said: “From what we can tell from the pictures and the information from the explosive ordnance disposal team, this is most likely an old German wartime sea mine.”
Two years ago, a second world war bomb containing 290lb of “high explosives” found in Portsmouth harbour was towed out to sea and detonated.