The feature McCartney dressed in a pro-vegetarian t-shirt under the strapline: "I am Paul McCartney and I am a vegetarian".
The McCartney ads are the organisation's latest spots in a long running celebrity-endorsed campaign, which has so far been backed by Heather Mills, Alicia Silverstone, Forest Whitaker and Pamela Anderson, among others.
In the spots, McCartney explains how he chose to be vegetarian after a fishing trip made him realise that the life of the fish was as important to it as his life is to him.
The ad's accompanying text says: "Many years ago, I was fishing and I as I was reeling in the poor fish I realised, 'I am killing him -- all for the passing pleasure it brings me'.
"And something inside me clicked. I realised as I watched him fight for breath that his life was as important to him as mine is to me."
The campaign for , which is one of the world's largest animal rights organisations, forms part of its latest drive to encourage people to turn vegetarian, which it claims would help tackle climate change and prevent famine, as well as ending cruelty to animals.
The campaign comes ahead of in the UK, which takes places between May 19-15 and is organised by the Vegetarian Society. The annual awareness-raising campaign, now in its 16th year, promotes vegetarian food is being sponsored by Cauldron Foods this year.
For more details about National Vegetarian Week 2008 visit the the