The appointment, by Scottish Borders Council, gives Scott Wilson responsibility for multi-disciplinary design, requirements definition, reference design and construction supervision up to 2011, when the scheme is due to open. Work begins immediately.
Waverley Railway Project is will link Endinburgh Newcraighall to Tweedbank in the Central Borders via 47km of track and seven new stations.
The line will serve around 200,000 people in the Scottish Borders and Midlothian, two of only three mainland areas in Scotland not currently served by a passenger railway.
Geoff French, Scott Wilson Chairman, said, "We are pleased to be awarded this contract win which reaffirms our reputation for delivering major multi-disciplinary rail projects. We look forward to contributing to this project and working closely with the partnership."
The £135M project is promoted by Scottish Borders Council, the City of Edinburgh Council, Midlothian Council and Scottish Enterprise Borders, with most of the funding coming from the Scottish Executive.
The Project is seen as the first phase in reinstating Edinburgh to Carlisle rail link, closed in 1969.