Newark and Sherwood District Council wants to restore Newark's old Magnus buildings into a museum incorporating an English Civil War gallery.
The council has applied to the Heritage Lottery Fund (HLF) for a £2.8m grant to support the £4.43m project.
The oldest parts of the buildings date to 1529.
The 1646 siege in royalist Newark, during the civil war, led to the final demise of King Charles I, and the start of English democracy.
The council wants people to join a steering group to help shape the plans.
The museum would house other collections from the district, including the Newark Torc which was bought by the council for £350,000.
The ancient Celtic gold necklace dates to 250 BC and was found by an amateur treasure hunter near Newark in 2005.
Plans have been unveiled to turn historical buildings in a Nottinghamshire town into a national centre for the civil war.