Iain Gray MSP said the contract on which the scheme was based was an “utter catastrophe”, as he backed calls for an investigation to be held “immediately” after the network launches next year.
The ex-Scottish Labour leader, who approved the £365million funding, said local authorities across Scotland had to learn from the cost overruns and delays which have dogged the landmark project.
He echoed cross-party demands from the inquiry, ahead of the launch of the line early next year.
Eventual costs rose to £776m with £550m supplied by the Scottish Government and the remainder borrowed by Edinburgh City Council.
Mr Gray addressed the project as the issue was debated by business leaders at Holyrood last night, and said the issue must be dealt after the launch in early 2014.
“My confession of guilt is that I was the enterprise and transport minister that provided the initial funding of £365m for Edinburgh to take the tram forward”, he told members of the Federations of Small Business at the Scottish Parliament last night.
He said that Edinburgh had qualified for the criteria but that the scheme had been badly handled, comments echoed by Lothians MSP Gavin Brown and Green MSP Alison Johnstone.
“It was an important process because Edinburgh is our capital city had a particular problem which was holding it back with the congestion and lack of a mass transit system.”
But he added: “I have to admit the delivery of the project has been an utter catastophe, from beginning to end and my review of the contract...is pretty much the same.
“The inquiry is crucial and to be honest i would have liked to see it start earlier.
“There is a huge strategic question for Scotland here, as every other city in Europe can deliver a transport system like the tram network, but somehow in Edinburgh and Scotland we cant.”
Marco Biagi, the Edinburgh Central MSP, representing the Scottish Government, said the government would “relish” the opportunity to determine what went wrong.
“The sooner the better but we have to wait until the tram project is completed and running.
“But this is not somethibg the First Minister has any fear about. I relish looking ahead to the prospect of this inquiry because there are some very serious questions about how the project was conceived at the starts about the levels of optimism that were shown.”
He added: “The long history of the tram project is going to be a test case for decades...to come of how not to do public projects.
“What kind of contract is it that get drawn up by where you find yourself with an option of completing the tram line at two-thirds of the original tram line at 50 per cent of the original cost, or cancelling the whole line for 20 per cent of the cost.”