Following a triumphant return to the Oberhausen Sea Life Aquarium in the western German city in July, Paul was rewarded with his own replica World Cup trophy garnished with his favourite food - mussels.
Paul used mussels to make his World Cup predictions for each game by choosing one from the two jars bearing the flags of opponents.
There has been recent rumours of retirement, along with offers to purchase him, but Tanja Munzig, spokseperson at the German aquarium, insisted that Paul would "step back from the official oracle business".
However, with his country of birth looking to stage the Fifa tournament in eight years, any thought of a rest seems to have been put on hold.
Nicola Hamilton, manager at Weymouth Sea Life Centre, said: "Paul has spent the last two years of his life in Germany, but he is definitely a proud Englishman and is therefore delighted to put his support behind England 2018.
"We have had a number of football approaches from around the world but Paul was only ever going to choose his homeland.
Will Paul be predicting success for England in 2018?
"With his predicting days behind him Paul is now concentrating on a number of new projects and the England 2018 campaign is something we are sure he feels passionately about. Becoming an official ambassador for the bid is an honour for Paul and everyone here."
Paul joins a list of celebrities supporting the bid that includes England players David Beckham and Rio Ferdinand, 2008 Formula 1 world champion Lewis Hamilton, and musicians Noel Gallagher and Sting.
Barnes, a former Liverpool and England midfielder and fellow 2018 ambassador, added: "After his success during South Africa 2010, Paul is undoubtedly one of the biggest names in football.
"I predict that huge numbers of people will follow Paul's lead and back the bid. Since our launch last year, more than a million football fans have officially shown their support, including some of England's most famous names.
"With the decision date fast approaching it's now more important than ever to get behind England 2018."
England is battling with Russia, the United States, Australia, and joint bids from Spain and Portugal, and Holland and Belgium for the right to host the 2018 World Cup tournament.
The winning bids for 2018 and the 2022 tournament will be revealed on 2 December.
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