Councillors in the Surrey town, located on the banks of the River Thames, voted for the change last year after consulting local residents.
They hope the new name will attract business and end the town's association with Sacha Baron Cohen's spoof rapper Ali G, who famously hailed from Staines.
It officially became Staines-upon-Thames at 2pm today (May 20). The change was marked with a day of celebrations, including a regatta.
"Ali G may have had a role, but I think it goes back further than that," Councillor Colin Davis told BBC News.
"I regard Ali G as someone who put Staines on the map, we're just telling people where it is."
However, critics including the town's football club have branded the move "pretentious". Steve Parsons, club secretary of Staines Town Football Club, campaigned against the change.
He said: "The council have decided they don't want to be linked with the Ali G Show.
"But the one they need to worry about is Keeping Up Appearances, where Mrs Bucket changed her name to Bouquet. I think it is as pretentious as that."
Alex Tribick, chairman of the Spelthorne Business Forum, defended the change, saying: "It's not pretentious, it's progress and the fact of the matter is there was a public consultation that returned with a two to one majority in favour of a change."
Dame Sarah Goad, the Lord-Lieutenant of Surrey, was responsible for officially changing the name.
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