The facility, which tenants have named the Rainbow Room, has been built at the Brockburn Road Very Sheltered Housing Complex, Pollok.
Tenants will be able to hold social activities in it, such as art and crafts classes, knitting bees and a pool competition.There is also a new decking area in which the 57 tenants to relax.
GHA's South Area Committee funded the project.
Work started last November and took nine months to complete.
Ms Lamont was joined at the opening by GHA chairman Gordon Sloan and representatives from GHA's south area committee.
The Glasgow Pollok MSP said: "It is a pleasure to be part of this event.
"We all know the importance of keeping active and involved and this sunroom allows tenants to come together socially, preventing the isolation many older people fear."
Annette McLinton, 75, and her fellow residents played a key role in the overall design of the new room.
She said: "We are all pleased, It is so comfy. We even got to choose the name, the colour scheme and what went into the room. GHA has been very good to us."
Mr Sloan believes the sunroom will make a difference to the tenants.
He said: "It is a fabulous complex. I have been lucky to have visited a number of similar rooms in our other complexes and I would say this is the best.
"Some tenants have problems with mobility and are not able to get out and about, but the Rainbow Room means they do not have to go far to keep in contact with their friends."