The Featherston Gateway complex, including the Supervalue supermarket on Fitzherbert St, was formally opened on Saturday morning.
The Trust House project took 14 months to convert and extend the original Four Square grocery store on site to a supermarket, relocating the Gusto cafe, Bottle-O bottle store and Post Shop and Kiwibank under the same roof.
The engineers managed to keep the grocery store operating throughout the build, transitioning to a Supervalue without major disruption to customers.
South Wairarapa Mayor Adrienne Staples cut the ribbon to formally signal the project's completion.
She said it had been exciting to see the complex created, which was "an awful long time coming.