The colourful artwork has been painted on the outside of one of the unused buildings at the City Museum in Portsmouth.
Street artist ATM was asked by the Hampshire and Isle of Wight Wildlife Trust to create the mural to celebrate the marine life in the Solent.
The cuttlefish, which can change colour and patterns, breed in the sea grass beds in the Solent every spring.
Lianne de Mello, from the trust, said: ‘This mural was about raising awareness to people of the marine life we have in the Solent.
‘We liked the idea of bringing wildlife into the cities.
‘ATM is known for his wildlife artwork. He normally paints birds on the sides of buildings but he was keen to try a marine theme.
‘He was really interested in the cuttlefish so decided that’s what he would paint.’
Councillor Linda Symes, cabinet member for culture, leisure and sport at Portsmouth City Council, and Portsmouth South Labour MP Stephen Morgan went to see the mural being unveiled on Saturday.
Members of the public also stopped to have a look at the artwork on Museum Road.
It took three days for ATM to complete and he had to work in the rain to get it finished in time.
He said: ‘The Hampshire and Isle of Wight Wildlife Trust got in touch about their project and I was happy to be a part of it.
‘They gave me a number of creatures to pick from but there was something about the cuttlefish. Its colours and movements are amazing.
‘It was a push to get it done because of the weather.’
Cllr Symes was impressed with the finished painting and the reason for the artwork.
She said: ‘The mural has brought something vibrant to that building and it is brilliant to see it promoting what we have living in the Solent.’
Mr Morgan agreed. He added: ‘There is so much living in the Solent and we shouldn’t forget about the wildlife on our doorstep.’