A Crufts spokesman said the hugely irresponsible stunt had scared the dogs and put their safety at risk.
Yvette Short, from Edinburgh, clutched her Best In Show whippet, called Tease, as security guards subdued the protester at the NEC in Birmingham.
The intruder was carrying a banner bearing the logo of PETA (People for the Ethical Treatment of Animals).
The crowd booed before breaking into applause as he was taken away.
A Crufts spokesman said It appears that protesters from PETA gained unauthorised access to the ring in the main arena at Crufts, and in doing so scared the dogs and put the safety of both dogs and people at risk in a hugely irresponsible way.
Our main priority at the moment is the wellbeing of the dogs that were in the ring, who are looked after by their owners and show officials.
The NEC Group have extensive security procedures in place at Crufts and we, along with the NEC Group, will be reviewing what happened as a matter of urgency.
PETA UK later posted a clip of the incident on Twitter and claimed activists were protesting against extreme breeding and carrying banners which said Crufts Canine Eugenics.
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.
News Source SkyNews