Contractors will dig up the road in Tower Place on April 2 to carry out diversion of utility pipes and cables in an exercise which will serve as a trial for similar work along the route.
It comes after Transport Minister Tavish Scott announced that the Scottish Executive had given approval in principle to the draft business case for the Capital's tram scheme.
And it was confirmed for the first time that people over 60 and the disabled will be able to travel for free on the trams.
That decision has always been up in the air as ministers were said to fear that agreeing to free travel for pensioners and disabled people would mean having to take the costly step of extending it to the Glasgow underground as well.
Mr Scott released the first 60m of funding to allow work to get going on utilities diversion on phase 1a of the scheme, from Ocean Terminal to the airport.
Ron Hewitt, chief executive of Edinburgh Chamber of Commerce, today welcomed the news. "The talking's over," he said. " It's time to get on track. Edinburgh and Scotland's economy will benefit from this essential building block in a transport system fit for the 21st century. This scheme will deliver for Edinburgh and connect our waterfront with its city centre and airport.
"However, citizens and businesses are going to have to be patient during the inconvenience of the construction process. The reward will be a clean fast efficient passenger service appropriate for our Capital city and its development ambitions."
The work in Leith is expected to last up to three weeks. Other preparatory work will be carried out at the site of the planned tram depot near the Gogar roundabout.
And the main utilities diversion work will get underway in June.
Council transport company TIE said it was not yet known which parts of the route would be done first, but it was likely work could be carried out in several different areas at the same time.
A single contractor, Alfred McAlpine Infrastructure Services, was given the job last year of moving water, gas and electricity pipes simultaneously to avoid repeatedly digging up the same stretch of road. Approval for the final business case is expected in September.
Announcing yesterday's decision, Mr Scott said: "Trams will give passengers a safe, environmental travel choice, a choice which will see reduced congestion and reduced emissions. The utilities agreement that has been put in place is the right approach. Allowing a single contractor to do all the work will minimise disruption in the Capital, save money and ensure the delivery of the project. That is welcome news for Edinburgh.
"Dependent on the scheme progressing well, the final business case will be assessed in the autumn."
A spokeswoman for the Scottish Executive confirmed that trams would be included in Scotland's free travel scheme.
She added: "To achieve its objectives and to be financially viable, concessionary travel would need to be available on the tram.
"It is therefore our intention to amend the national concessionary fares scheme to include Edinburgh tram."
It is understood the final business case will be expected to include costings not yet available for the tram cars and installation of overhead lines.
The Executive said phase 1b - from Haymarket to Granton - was dependent on savings being made on 1a.
Edinburgh West Liberal Democrat MSP Margaret Smith said: "This is good news. The minister has indicated he is still in favour of the project but is not prepared to write a blank cheque.
"I don't think TIE has fully made their case yet and there are question marks over the viability of 1b in terms of patronage.
"I wouldn't be surprised if they are not told to prove they can run the first part of the line before 1b is approved. This is a step forward but the minister is right in terms of insisting this is properly project-managed."
But trams opponent SNP Lothians MSP Kenny MacAskill accused the Executive of trying to foist an unpopular scheme on the Capital before the elections.
"This is a major project that should be decided after May 3," he said. "They have wasted enough money to date without now starting on digging up the roads, causing huge disruption to the life of the city."