The 500-pupil primary, in Carntyne, had previously used the school's dining hall for games.
But – thanks to a recent refurbishment –youngsters now have a state-of-the-art facility to boost their sporting achievements.
And, with the Commonwealth Games just around the corner, head teacher Laura Mclean said the investment could not come at a better time.
Mrs Mclean said: "This is a lovely new sport facility for our young people, and the pupils who used the gym on the first morning it was ready were just fascinated by the facilities.
"Previously we had to use the dining hall to double up for sport but this new gym hall has gives us lots more room and lots more opportunity for sport.
"We can now offer basketball and netball to the pupils as we have hoops, and lines are drawn for five different sports.
"We are an East End school and with the Commonwealth Games on their way we want to be as best placed as possible to promote sport and get involved."
The school held a special assembly to mark the opening and children invited Margaret Curran MP as a special guest.
And they also welcomed Commonwealth Games mascot Clyde, who helped unveil the new building.
The extra space also means teachers can hold assemblies with the whole school together, something not possible in the old dining hall.
Last week St Timothy's hosted head teachers from Sweden, France, Greece and Luxembourg to see how the school is creating a Commonwealth Games legacy.
Mrs Mclean added: "Creating a Commonwealth Games legacy is very important for our school and the head teachers from Europe were really interested to see what we're doing.
"They are hoping to return and bring pupils with them too."
In August, the Evening Times told how parents claimed the school's playground was like a "building site" with youngsters left to play near diggers.
Education bosses pledged to make improvements to the building and sport facilities with an annexe built on part of the playground.
As part of the refurbishment the school building was upgraded with new windows.
Stephen Curran, executive member for education and young people, said: "I know that the £1.3 million upgrade to the school is welcomed by the parents and the school.
"The new facilities will greatly enhance the school building and I hope the children and staff enjoy the new sports hall for many years to come."