Approval has been given to replace sliding sash windows with new timber ones at 11 Bigby Street.
The grade two listed building is more than 200 years old and occupied by the Hetts Johnson Whiting solicitors' practice.
The application sought the go-ahead to replace life-expired hardwood frames "like for like" so it does not materially affect the character of the building.
North Lincolnshire Council's conservation officer advised planning colleagues that the suggested replacement would be appropriate to the age and character of the listed building.
Brigg Town Council supported the application made by the firm.
- North Lincolnshire Council has also granted another applicant's request for permission to erect a single storey side extension and extension to a garage at 13 Eastfield Road, Brigg.
