Major construction was halted several years ago following a dispute over who should pay for additional costs.
The diversions are in preparation for remedial works on the road surface and buses, taxis and cyclists will be diverted along George Street from 19 September, with all other traffic being rerouted along Queen Street.
As part of the mediation process earlier this year, the Consortium agreed to carry out further work in Princes Street at no extra cost to the project.
The work is due to be finished by July 2012 and the City Council said no work would take place during the Winter Festivals.
The local authority was given a deadline of 14 September to renegotiate a deal with the company BilfingerBerger.
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The original budget for taking the line from Edinburgh airport through the city centre to Newhaven, in the north of the city, was £545m.
However the cost of the tram project grew steadily, with estimates for partial completion to St Andrew Square reaching more than £830m.
The city council will have to borrow up to £231m to take the line into the city centre.
Council Leader Cllr Jenny Dawe said: "This is a first step in getting the works moving forward. We recognise the impact of putting the diversions in place. Disruption to visitors and shoppers on Princes Street will be kept to a minimum and we have liaised closely with local businesses to ensure the diversion goes as smoothly as possible for them.
"Our message is that Edinburgh is very much open for business and this will be communicated to the public through advertising, on-street signs and maps in the run up to the diversions going into place. The measures to avoid a clash with the very important winter festival season also remain in place."
Chief Executive Sue Bruce added: "It's essential for the project that we begin work soon, and for everyone in the city centre the certainty that it will be finished as soon as practicable is important. A huge amount of effort has gone into this and all parties are working hard to ensure we make headway for the short and long-term benefit of the city."
See Edinburgh Tram Decision Could 'Screech To Halt'
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