CH2M Hill has secured work on the £86M Shieldhall Tunnel in Glasgow.
The consultancy will provide technical advisory and site supervision services for the Scottish Water scheme.
The 5km-long, 4.65m-diameter sewer tunnel on the south side of Glasgow is designed to improve water quality in the River Clyde and its tributaries.
A joint venture of Costain and Vinci Construction was last week named preferred bidder for the main contractor package.
Construction is due to start later this year, with completion scheduled for early 2018.
CH2M Hill managing director of tunnels and earth engineering Martin Knights said: “This announcement is another great example of the commitment Scottish Water is taking to improving the environment in Glasgow.”