The veteran Independent MSP won the support of former Scottish Government minister Stewart Stevenson yesterday and called on others to endorse her plan for legal action.
She lodged a Holyrood motion last week urging the Scottish Government to change the law in a bid to try the former prime minister over his role in taking Britain into an "aggressive" war with Iraq.
The move followed a call by Archbishop Desmond Tutu to prosecute Mr Blair and former US president George Bush.
It has already attracted the support of six MSPs, but the Scottish Government has ruled out action, arguing that Holyrood does not have the necessary powers. Asked if she now planned to bypass the Government and bring a Member's Bill before parliament, she said: "If I don't get broader support from parliamentary colleagues I don't think there is any sense in bringing forward a Bill.
"But if I feel support is widespread enough to justify it I will press for a member's debate and it is amazing what can happen after that. If I got 25 signatures I'd start thinking about it then."
The Lothians MSP welcomed the support of Mr Stevenson, the former climate change minister who retired from the Government last week, and said the backing of one of Alex Salmond's closest political allies should encourage others to follow suit.
She added: "I did it not just for the obvious reason but to declare to people in the Middle East and Africa that we are willing to treat leaders who get it wrong in this country in the same way we treat leaders from other countries."
In addition to Mr Stevenson, five other SNP MSPs have backed the motion: Annabelle Ewing, Gordon MacDonald, John Finnie, Jim Eadie and Chic Brodie.
Mr Brodie said: "I think it is worth exploring if we can bring Tony Blair to trial, and certainly I would support us having a debate at Holyrood.
"So many British and Iraqi families have suffered and I think we still need to question what it was all about."
Ms MacDonald's motion calls on MSPs to support Nobel Peace Prize winner Archbishop Tutu's demand for Mr Blair to be prosecuted.
She believes he could be tried in Scotland if Scots law incorporates a principle of international law making it illegal to wage an "aggressive war with the intention of regime change".
Scottish Labour have dismissed the move as a "stunt", claiming it is designed to distract attention from the SNP Government's economic record.
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