Cerys Cooksammy-Parnell, from Northampton, scored a mind-blowing 162 on the Cattell B scale.
The schoolgirl sat the supervised test with her father Dean, 45, who is already a member of the elite intelligence club with an IQ of 142.
Her lawyer dad thought she'd 'fluffed it' – but he was very wrong!
While Cerys was pleased with her score, she was more pleased to have beaten her dad.
"When I was applying to Mensa he said 'oh I'm already in Mensa, Cerys', he was like showing off a bit, so it's good that I got my own back on him," she said.
Having discovered her gift, her parents are now considering whether to let her continue living a normal life or 'push her intellectually'.
"I was expecting her IQ to be upwards of 145, there's no doubt about that, but to actually hit the maximum it was a surprise. We're all really excited and proud of her," added Mr Cooksammy-Parnell.