The Hall for Cornwall Trust is seeking an architect for a major overhaul of its Grade II*-listed Truro venue
Planned to complete in 2019, the project will upgrade and enlarge the historic auditorium and its front and back-of-house facilities.
The arts centre is based inside a former municipal complex constructed in the neo-classical style in 1846.
Constructed from Carn Brea granite, the former courthouse and town hall was converted into a public hall in 1909 and later transformed into a theatre following a fire in 1914.
The building was restored again in 1997 following several decades as a flea market. The current centre draws around 180,000 visitors every year and features a restaurant and coffee shop.
The winner of the estimated £950,000 contract will develop existing plans from RIBA Stage 2 onwards.
The deadline for requests to participate is 3pm on 27 May.