The deal is expected to be worth approximately £560m to the joint venture, which is called ESD (standing for Efficient Service Delivery).
The framework starts immediately and runs for six years.
Works will include design and build projects, both new-build and capital upgrades, for the client's water and wastewater treatment programme.
Scottish Water chief executive Douglas Millican said: “As well as being good for the economy, our investment programme will enable us to build on improvements to customer service around Scotland, while protecting and enhancing the environment. Appointing ESD to the programme will help ensure our customers continue to receive fresh drinking water and have their wastewater treated to the highest standard, while benefitting from one of the best value water utilities in the UK.”
ESD chief operating officer Tony Collins said: “ESD stands for efficient service delivery, which is what this joint venture is all about. Through collaborative working ESD will make a significant contribution to the environment and wellbeing of communities across Scotland whilst also delivering a capital programme for Scottish water which provides significant financial efficiencies.”
Galliford Try executive chairman Greg Fitzgerald said: "We are delighted to have secured such a substantial amount of long-term business in a key sector for us. We look forward to building on our relationship with Scottish Water and bringing the benefit of our experience of collaboration across the UK water sector to Scottish Water and its customers."