Led by conductor and Oswestry School's director of music Aled Philips, the choir from the Shropshire/North Wales border won over all four judges on the ITV show in the auditions earlier this year.
The John's choir, based at Rhosllanerchrugog between the Shropshire border and Wrexham, practices once a week in a cow shed. But the choristers are just at home in bow ties in concert halls across Britain.
With singers from both North Wales and Shropshire in the choir, they got together through their love of singing.
The choir was formed in 2016 when members collaborated to celebrate the lives of their former conductors, John Glyn-Williams and John Tudor-Davies.
Members are urging supporters to register to vote before the public get their say at the end of the 8pm show.
The singers went on social media to say: "Please vote for us and support us tomorrow night! You can register online to vote now to be ready for when the vote is open, itv.com/vote/bgt. We can't believe it, and we can't wait."
The choir's last appearance brought judges Bruno Tonioli and Amanda Holden to tears.
Bruno told the choristers: "I'm telling you, the blend of your voices, the balance, the harmonies – it was divine. I felt I was in music heaven. Perfection."