Booth, the half-sister of Blair's barrister wife Cherie, is in Malaysia for lectures organized by Viva Palestina, a British-based organization associated with controversial politician George Galloway.
Asked whether Blair should be arrested and sent to the International Court of Justice in The Hague for war crimes, Booth replied: "Absolutely. He misled the British people and took Britain to war on a lie."
The conflict in Iraq was "an offense", she told reporters after a speech at a Malaysian university, saying it was organized well in advance between Blair and the United States leadership.
Booth has been a vocal opponent of the war in Iraq, and a supporter of the Palestinian cause, and in 2008 travelled with other activists to Gaza by ship to protest against Israel's blockade of the territory.
Booth in Malaysia. 'Don't you miss the pubs?' (Photo: AFP)
The 43-year-old, who wore a black headscarf that tightly framed her face as she gave an address on "Islam from the perspective of Western women", discussed her own conversion which took place 15 weeks ago.
"My friends think I was naive and stupid, they have rubbished me so much," she said. "Really, joining Islam is not a trendy thing to do.
"Friends ask me, don't you miss going to the pub?"
But she defended her decision, which came after a trip to Iran in September 2010, and said that perceptions about Muslim women were incorrect.
"I sat down in the mosque in Iran, there was such tranquility. I had the compulsion to pray and from then on I knew I was a Muslim," she said.
"Muslim women are not oppressed, it is Western women who are oppressed... Western women are bored, lonely and oppressed."
Blair recently testified at the Iraq war inquiry, expressing regret at the death toll from the 2003 conflict and addressing the condemnation he faced following his first hearing last January when he said he had "no regret" about removing Iraqi dictator Saddam Hussein.
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