The ex-prime minister said he disagreed with the Labour leader's handling of the issue, warning that the country could become a breeding ground for extremists if Bashar Assad's regime was not confronted.
However, he also admitted the long and bloody struggle that followed the invasion of Iraq had left Britain "hesitant" about getting involved.
In an interview with the BBC, Mr Blair said he was "disappointed" the Commons had rejected a Government motion paving the way for direct action. "This is something where I just have to disagree with the leadership of the party," he said. "I know it's a difficult position for political leaders to be put in when they have to take decisions like this."
Mr Blair said without foreign intervention "you will have an Assad-dominated state, and that means in this instance an Iran-dominated state, probably around the borders of Lebanon and controlling most of the wealth of Syria".
Mr Blair said there was no question that chemical weapons had been used, and Assad's forces were responsible.
In a message on Twitter, the former deputy prime minister Lord Prescott said: "I've always respected Tony Blair but he's wrong on Syria and Ed is right. "