Writing in a Sunday newspaper, the PM's support has come in the wake of a series of extremist activities, which has drawn worldwide attention to the conflict between the two parties and has threatened the future of animal research conducted in the UK.
In his article, Blair condemned the "appalling" activities of animal rights extremists and stated he would sign the online People's Petition backing medical research.
The petition, which has been set up by The Coalition for Medical Progress (CMP), enables members of the UK public to express their support for medical research that uses animals as subjects.
The move is in response to recent news reports that have unfairly portrayed animal research as an unnecessary process, which has been carried despite mass protests from the general public.
The National Anti-Vivisection Society chastised the Prime Minister for taking such a "hugely irresponsible step," adding that they were "deeply concerned and disappointed to hear he had signed an online petition in favour of animal testing."
"We understand this petition has only 13,000 names, as compared to over 20 times that number of people who support animal welfare groups on non-animal research, plus the overwhelming public support for replacement of animals in testing," said Jan Creamer, chief executive.
"This petition is being run by an extremist group of vested interests representing a very narrow area of medical research that wants to see the UK continue with an outdated method of research as opposed to taking up more advanced, non-animal scientific methods."
Animal testing has been thrust into the spotlight this past week after private GlaxoSmithKline (GSK) shareholders were sent threatening letters from extremists warning them to sell their interests in the company or face public identification.
Even more horrifying was the story of four animal rights activists, who were jailed for waging a campaign of terror against a family, which included digging up a grandmother's grave.
Activists who aimed to stop them breeding guinea pigs for research targeted the family of the deceased for six years and culminated in the theft of the grandmother's body from a graveyard in October 2004, which appalled and disgusted people nationwide.
The British Union for the Abolition of Vivisection took a less harsher stance, commenting that: "The Prime Minister is right to take a tough line against extremism but wrong to think that needs a tough line in favour of animal experiments."
They added that: "Mr Blair seems to be blindly backing the animal experimenters in the mistaken view that what's needed is solidarity with them: what's actually needed is a cool and objective look at the profound animal suffering and outmoded science that animal experiments represent."
>GSK chief executive Jean-Pierre Garnier, also voiced his support commenting that he was greatly encouraged by his personal commitment, and that of his government, to ensuring an environment in the UK that is conducive to the research and development of vital new medicines.
The Association of the British Pharmaceutical Industry (ABPI), also voiced similar support for the Prime Minister's actions welcoming the Prime Minister's pledge that further legislation against extremists would be considered if necessary.
"At the moment, the number of violent incidents seems to be on the decline, but anonymous threats to ordinary shareholders is yet more evidence that there are people in this movement who will stop at nothing," said Richard Barker, Director General of the ABPI.
"It is reassuring to see that the Prime Minister is willing to consider any other action that may become necessary."