The project, which launched in June last year, has seen changes to road layouts, pavement widening, new pedestrian crossings and additional disabled parking and loading bays.
During the work, contractors laid over 7,250 sq m of road surfacing material, laid 92,000 brick pavers and installed 31 new light columns.
The scheme, carried out by East Sussex Highways, has transformed an area of the town centre including High Street, Vicarage Lane, Vicarage Road and George Street.
The project was funded by contributions by housing developers and £1.3 million from East Sussex County Council, which delivered the scheme in partnership with Wealden District Council, Hailsham Town Council and Hellingly Parish Council.
Cllr Nick Bennett, county council lead member for transport and environment, said: “We’re delighted the scheme has completed and the improvement is clear for all to see.
“This scheme was all about ensuring Hailsham could cope with increased traffic from the new housing developments planned in the area in the future.
“But it was also about improving conditions for pedestrians and ensuring we have a modern, vibrant town centre which will continue to flourish.
“While our contractors have done everything possible to minimise the impact of the work, we do realise there has been some disruption and we’d like to thank residents and businesses for their patience and understanding.”