Bosses at the Fuse Youth Cafe in Shettleston hope the work will increase footfall by 200 people a week and draw more adults to use the facility.
Plans for the building include an extension at the back and refurbishing the front to make better use of the space available.
The work is being funded by a grant from the Big Lottery Fund.
Work is due to start in April and should take about six months to complete.
Gerry Baldwin, project manager at Fuse Youth Cafe, said he hoped the centre could remain open for most of the time the work is being one.
At the moment the centre is open six days a week and hosts fitness classes, gigs, a radio station and cooking sessions, as well as running a volunteer programme for 10 to 25-year-olds.
For local unemployed young people there is also a job club and careers advice service.
In 2012, the Fuse Youth Cafe was a finalist in the Health and Wellbeing Award at the Evening Times Community Champions East End Awards.
The building was formerly one of the roughest pubs in Glasgow's East End, The Sheiling. Gangland figure Gordon Ross, 36, was stabbed to death after being lured out of the pub in September 2002.
He was found injured on the pavement outside and died later in hospital.
Shettleston Housing Association paid £270,000 to acquire the building in 2006.
Two years later it was given a £250,000 revamp to make it ready to host the youth cafe, but Mr Baldwin said the job was never fully finished.
Now those faults are going to be put right and the building is to be opened up for the whole community to make use of.
A new reception area will be created to give greater access to the rest of the building to allow classes to be held in separate halls.
A community room will also be built and the toilets will be upgraded.
Mr Baldwin said: "At the moment, the top floor of the building can't be used when there are young people in.
"But the extension will open up the whole facility.
"The toilets were never redeveloped in the original redevelopment and they are now being done.
"The front of the building will also be refurbished.
"A lot of it is about stuff that hadn't been done previously and making it more appealing to the community.
"We want to extend the provision for young people and expand to other age groups.
"The idea is to be available for community groups, putting on fitness classes and more adult centred provision."