East Anglian firm Mills & Reeve has won the contract to provide legal services to Leicester City Council.
Mills & Reeve beat four local firms for the work.
The selection process was "arduous" according to Nicholas Hancox, head of Mills & Reeve's local authority team.
"They were very thorough about it. Some people do it all on paper, and some want you in there to discuss points of law, and Leicester wanted to discuss points of law," says Hancox.
The firm will work with the council's legal services department, with staff seconded to its in-house department.
The work includes both advocacy and advice on employment law, and general civil and criminal litigation work.
Hancox says: "There is a natural tendency, all things being equal, to go to a firm that is round the corner rather than 30 miles away. But the experience Mills & Reeve has of working with local authorities is something that the local firms possibly do not have."
Hancox believes the contract is evidence of the westward spread of Mills & Reeve's local authority work since it opened in Birmingham in August 1998.
"I've got some dots on the map in front of me showing where our clients are, and it's definitely heading westwards," he says.