Weymouth and Portland Borough Council has already agreed in principal to relocate from its North Quay offices, with the bulk of staff moving to South Walks House in the county town.
The two authorities are currently working in partnership with a joint officer structure.
The executive committee was told that South Walks House currently accommodates 258 staff with space for an additional 100 and there is a proposal to move 96 from North Quay.
There will be some minor alterations required at the Dorchester office and Weymouth and Portland Borough Council is being asked to contribute around £60,000 a year towards the operational cost of South Walks House.
Members were told consultation would take place with staff and unions over the summer and it is expected that the first staff from Weymouth would arrive in Dorchester before Christmas, with a phased approach for the rest of the arrivals.
Cllr Alan Thacker said: “It’s good we can bring all the staff into a much more modern working environment. It’s better for everybody that that happens and it’s one more benefit of a partnership.”