Kate Bosworth, Matt Lucas, David Walliams, Kelly Osbourne, Moby and Sophie Ellis Bextor were just some of the stars who descended on London's St James' Park to show their support for Paul, daughters Stella and Mary, and son James as they called for 'Meat Free Mondays'.
And making a surprise appearance was Yoko Ono, the widow of 66-year-old Paul's late band mate John Lennon.
The campaign aims to encourage people to go veggie at least once every seven days to help combat climate change.
It was prompted by a UN report that says meat production is responsible for 18 per cent of greenhouse gas emissions.
Acknowledging some meat eaters would find it hard to cut it out altogether, Beatles star Paul - introduced to vegetarianism by his late wife Linda McCartney - said: "I thought this was a great idea. To reduce your meat intake maybe by one day a week, and this would seriously benefit the planet."
Described as "an achievable goal" by photographer Mary, the initiative is also being backed by Coldplay's Chris Martin, Kevin Spacey, Joanna Lumley and Sir Richard Branson.
"I love eating meat, but I love our planet even more, so I will join this campaign and stop eating meat at least once a week," the Virgin business tycoon said.
Click here to visit the Meat Free Mondays website