The work will require machinery to access the site across the historic castle bowling green, which in turn will require removing a small section of wall at the entrance to the bowling green from Castle Precincts.
Machinery will then need to cross the gardens of two private residential properties to get to the site of the collapsed wall, which is on private land but is the responsibility of the county council. The work will be carried out later this week.
An East Sussex County Council spokesman said: “We’re sorry that this work will cause some disruption at the bowling green and for local residents, but we’ve examined all options and unfortunately this is the only feasible way of getting machinery to what is an extremely tight and difficult to access site.
“At present, there is a small part of the collapsed section of wall that is still standing but is in a precarious position and our contractors need to get in to make this section safe.
“We will unfortunately have to remove a section of wall dating back to the 1970s at the entrance to the bowling green to enable access but this will be rebuilt once work is complete.
“The machinery will be taken in across one small section of the bowling green and we will be laying down matting to minimise any damage to the grass.
“We have been in close contact with people who use the bowling green and nearby residents and thank them for their patience and understanding. We will continue to keep them updated.”
The council is working with partners including Lewes District Council and Historic England to investigate the original wall collapse last week, and to formulate a long-term plan for the site.