LGPS Central Limited will take over the first floor of the i9 development on Railway Drive, Wolverhampton, which was officially opened earlier this month.
The firm manages local government pensions assets and will employ 70 staff at the site. The ground and fourth floors of the building have been taken over by a new headquarters for the Department for Levelling Up, Housing & Communities.
Council chiefs have also revealed that an agreement is close to being finalised with another "big name" occupier for the site.
Wolverhampton Council deputy leader and city economy chief, Councillor Stephen Simkins, said the firm's decision to move to the i9 showed the "strong demand for top quality office space in the city".
He added that the block's location near to the railway station had been "a major selling point", and that following the success of the i9 and i10 developments the council was "looking at ways to develop more" office space.
Joanne Segars, Chair, LGPS Central Limited, said moving to the i9 would "ensure that we are fit for growth and operating in a way that positions us to achieve our ambitious future goals".