Hundreds of people gathered outside the QEII conference centre in Westminster to chant anti-Blair slogans and call for his arrest for war crimes.
But they did not have the chance to confront the ex-premier as he gave them the slip by arriving via a back entrance more than two hours before he was due to be questioned by the Chilcot Inquiry.
Protest organisers said they were "appalled" at the way Mr Blair had "sneaked" into the building.
Andrew Murray, chairman of the Stop The War Coalition, said: "This cowardly and deceitful entrance is typical of how the former prime minister sold the war to the country - behind the backs of the public."
Lindsey German, the group's convener, said: "Blair doesn't have the decency or honesty to face up to the public, military families, and Iraqis who will be here today in huge numbers to show their opposition to the war.
"He does not have the integrity to come and face the people. Sliding in by a back door entrance is typical of his lies, deceit and evasion."
Kate Hudson, chairwoman of the Campaign for Nuclear Disarmament, said Mr Blair should be arrested and put on trial for crimes against humanity.
"He should face a court. The way he arrived today was sneaky. He just does not want to face up to his crimes - it is an outrage."
Hundreds of police officers formed a cordon around the centre to keep protesters away from the immediate vicinity and the entrance, forcing them to stand on the pavement, shouting slogans including "Jail Tony" and "Blair lied - thousands died".
Many of the demonstrators wore T-shirts bearing the slogan "Jail Tony".
One group of protesters wearing Tony Blair masks and with fake blood on their hands carried a coffin bearing the slogan: "The blood price."
Saba Jaiwad, from an Iraqi anti-war group, said his fellow countrymen and women suffered "appalling" consequences as a result of the war.
"The Iraqi people are having to live every day with aggression, division and atrocities. Tony Blair should not be here giving his excuses for the illegal war, he should be taken to The Hague to face criminal charges because he has committed crimes against the Iraqi people."
Katherine Hamnett, a leading fashion designer who joined the protest, said she believed the way the UK was taken to war showed that the political system in this country had failed.
As Mr Blair sat down at the start of today's session, the anti-war protesters turned their backs on the conference centre to listen to names of civilians and military personnel killed in the conflict being read out, including babies and children, as well as British soldiers.
Mr Murray introduced the naming ceremony by repeating demands for Mr Blair to be arrested, adding that he expected more than 1,000 people to join the protest during the day.
Relatives of soldiers killed in the conflict, who sat through Mr Blair's evidence, left looking upset and angry, many saying they had learned nothing new.
Some said Mr Blair had been "smirking" and accused him of "disrespect".
One father walked out of an adjoining room where most of the families given access to the hearing were watching on a live monitor.
He left after less than an one hour, shouting out: "I can't take any more of this," and "it's a complete waste of time".
Sarah Chapman, from Cambridge, whose brother Sergeant Bob O'Connor died five years ago tomorrow, attacked Mr Blair's "smug appearance".
The former nurse said: "He is sitting with his back to the families, which I think is a mark of disrespect. There are a number of bereaved families simply looking at his back.
"He is being very adamant about his views, as we expected, but it is clear he did not share all the papers before the invasion with the rest of his Cabinet. I am disgusted by that."
Mrs Chapman said she had given up work as a nurse since her brother was killed and is now suffering post-traumatic stress.
"I feel as though I have been given a life sentence. I am now unemployed and many other military families have suffered."
Anne Donnachie, from Reading, whose 18-year-old son Paul was killed by a sniper in 2006, said she blamed Mr Blair for his death.
"From what I have heard, he is just denying everything. He will just not face up to the facts. I believe he made a massive mistake when he sent my son to Iraq."
Theresea Evans, from Llandudno, North Wales, whose 24-year-old son Llywelyn died in a Chinook helicopter crash in 2003, said: "I would simply like Tony Blair to look me in the eyes and say he was sorry. Instead he is in there smirking.
"At one stage he was laughing and smiling. That really hurt."
Londoner Harry Robinson, a member of the public who sat through Mr Blair's appearance, said: "I have just seen one of the finest performances by an actor the West End has ever seen. He should get an award."
The number of protesters mounted in anticipation of Mr Blair's departure from the conference centre.
John Rees, co-founder of the Stop The War Coalition, addressed the crowd, saying: "None of us in the anti-war movement have ever defended Saddam Hussein but Saddam Hussein is not the only Iraqi who is gone in 2010.
"There are another million Iraqis who are dead, dispersed and lost their homes and their families because of what that man did."
About 150 protesters stood facing police officers on Storey's Gate, chanting loudly and waving banners.
Clarence Bieris, 68, a union worker, said he came straight from work to take part.
He said: "He has been lying from the beginning. And the price we are paying is too high. People are dying.
"I wanted to come here to make sure he will get the message."
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