The council aims to bring separate plans to revamp the Market Square, Guildhall and Corn Exchange under one project worth up to £75m.
The council has set aside a budget of £55m for the work.
The bulk of spending will be channelled into conserving the Grade II listed Guildhall as a net zero-carbon building to save running costs and create a welcoming environment for the public.
At the Corn Exchange, the plan is to increase event capacity to 2,000 people.
The council says it needs to invest in the sites’ upkeep while generating income and reducing operational costs. It also seeks to make heritage buildings net zero.
Architect Cartwright Pickard has designed the scheme with Arup also on board.
Construction work is not expected to commence before October 2026 at the earliest.