Gemma Collis grew up in Buckinghamshire as a competitive athlete in multiple sports: figure skating, hockey, 100 metres running, and triple jump, in the last of which she hoped to compete in the London 2012 Summer Olympics.

[7] Gemma Collis married fellow British Paralympian Craig McCann in July 2017; both took the hyphenated last name Collis-McCann.

[7] In July 2021 she and three sportsmen, Piers Gilliver, Dimitri Coutya and Oliver Lam-Watson were identified as the British wheelchair fencing team who would compete at the delayed 2020 Summer Paralympics in Tokyo.

[10] Her selection followed 18 months when she did not compete due to the COVID-19 pandemic, including the closing of the Tokyo qualification window by the International Wheelchair and Amputee Sports Federation.

Her most recent gold came at the IWAS Wheelchair Fencing World Cup in Pisa in March 2023 when she beat China's Yuandong Chen in the final 15-7 to win gold, having overcome reigning Paralympic and European champion Amarilla Veres of Hungary in the semi-final.

[16] In 2022 she was presented a poster on 'The Power of Disability Sport to Change the Lives of Women with Disabilities' which used Wheelchair Fencing as a case study, alongside fellow IWAS Fencing Gender Equity Commission members Ksenia Ovsyannikova, Dominique Hornus-Dragne and Christina Massiala-Vaka at the International Working Group on Women and Sport World Conference held in Auckland.