Austin Mitchell will, from Friday, be known as Austin Haddock in honour of National Seafood Week.
The economy of Mr Haddock's constituency of Great Grimsby is heavily dependent on fishing and he hopes his name change boost trade for local trawlermen.
He has, however, admitted that he may revert to his given name because his family think he is "mad".
The idea for the stunt came from Young's Seafood, a major employer in Mr Haddock's constituency, but it has already led to some mickey-taking.
Mr Haddock, who is in Blackpool for the Labour Party conference, said: "I got in a cab this morning and the driver said: 'If you're Mr Haddock, you don't need a taxi to get to the conference centre - just hop in the sea and swim'."
Despite the urge to see it as a joke, the MP believes the new name can help his constituents.
He said: "The idea is to encourage people to think fish, cook fish, eat fish and buy fish.
"If they do that, it's good for the industry and good for Grimsby.
'Fun' idea
"I've signed the deed poll and it takes effect on Friday, for the start of Seafood Week."
Sadly, the people of Grimsby are likely to miss the opportunity to "Vote Haddock" at the next election as the name change is only temporary.
Mr Haddock admitted: "As long as it's fun I shall carry on, but I have to admit, I'll probably go back to Mitchell at the end of the week.
"My family think I'm mad."