Brandishing posters reading, "Crufts: Canine Eugenics", the protesters highlighted the suffering of dogs bred by humans to have grossly exaggerated features - all to meet The Kennel Club's "Breed Standards".
The male intruder was quickly wrestled to the ground.
It all kicked off just as the victor, a whippet called Tease owned by Yvette Short, was being announced at the NEC in Birmingham.
As the man ran towards Ms Short she grimaced, picking up the dog and holding the dog close to her.
A Crufts spokesman said the hugely irresponsible stunt had scared the dogs and put their safety at risk.
One of the two protesters brandished a sign saying "Crufts: Canine Eugenics" after disturbing the event while the victor (a two-year-old whippet bitch called Tease with human companion Jill Peak) was being announced.
Crufts and the NEC said security would be reviewed as "a matter of urgency".
"Our main priority at the moment is the well-being of the dogs that were in the ring, who are looked after by their owners and show officials".
It said there were two intruders and named them as members of the Vegan Strike Group, an organisation which claims to fight against animal abuse.
This protester was carried off by security guards as crowds applauded his removalHow is Best in Show victor Tease doing after the scare?
Owner Yvette Short from Edinburgh said Tease's victory was "incredible". Well done to security for tackling the intruder and the victor for grabbing her dog and running away, pure love.
The breeding of certain kinds of dogs "just adds to this animal overpopulation crisis that we have found ourselves in".