Based in Yorkshire and the North West, Strategic Team Group employs 120 staff and currently has 23 live sites.
Last year the firm reported revenues of £62m and delivered over 500 new homes.
The management team and staff at STG will remain in place, working within Partnerships to accelerate both businesses growth plans.
It will begin to trade as Galliford Try Partnerships Yorkshire from 1 July 2019.
The purchase supports Partnerships’ plan to target growth in key regions around the country to increase the supply of new homes.
Since becoming chief executive of Partnerships in 2016, Stephen Teagle also led the successful acquisition of Drew Smith, based near Southampton, to create a Southern region to the business and expanded existing regional businesses in the West, Midlands and London.
Teagle said: “We are really excited to have reached agreement with Strategic Team Group, which is a great fit for our growing business.
“It will enable us to expand our regeneration offering and help accelerate delivery in Yorkshire and the North West.”
Andy Watson, managing director of Strategic Team Group, said: “Galliford Try Partnerships is an excellent fit for STG and we believe the deal will help to accelerate growth in areas where we see real opportunity for housing supply, helping to deliver development objectives for clients.”