The five-storey development in Ashington part of a 10-year regeneration programme being led by Arch, a development company wholly owned by Northumberland County Council.
Galliford Try moves on site in January 2017 and is expected to take 18 months to complete the new council offices, employing up to 220 people in the construction.
The office scheme involves a smaller and more cost-effective building than the current council headquarters in Morpeth, which dates from 1981. The relocation saves on essential refurbishment and frees up the Loansdean site for a new school, retail and housing development. The council has calculated that it will save £16m over the next 25 years.
Northumberland County Council leader Grant Davey said: “‘This is a welcome next step in our Market Towns Initiative to regenerate and improve Northumberland’s towns. We’re pleased the scheme has now appointed a team to start work and can now progress for the benefit of the town, the county and the wider region."