Group Scout Leader, Bruce Martin, said the new building is "stunning" and serves 160 young people every week.
"It will be here for the next 40 years and it's something the whole community can use," he said.
"It's very exciting and the amount of effort that dozens of people have put in over the last 12 months is brilliant. To achieve this much in that time takes a lot of hard work from a lot of people and it has shown scouting at its best, which is people pulling together to help young people develop and allow them some where they can practice their scouting in a safe and secure place. It's a great success story."
The project, which was on the cards for nearly five years, cost around £250,000 and saw the old building revamped with a new roof, outer 'skin' to stop it leaking, new floor, toilets and storage areas. It was also extended by 20 feet.
The Scouts furiously fundraised to get the money together. In July 100 of them walked from Brownsea Island, the site of the first Scout group set up by Baden Powell, to Abbey House in Winchester, where Steve Brine was among a large group welcoming them back to the city.
Steve said: "I was delighted to mark this special occasion, not least because I was part of a large group welcoming them back from their epic walk last July. My congratulations to all the team who strived tirelessly to make the vision into a reality."
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Watch a special video of the event here