Sophie began paracycling after attending an open talent event in August 2020.[1] She won the bronze medal in the individual pursuit at the 2020 Summer Paralympics alongside Jenny Holl. She also partnered with Holl to claim silver in the women's road race B event during the 2020 Summer Paralympics.
She represented England at the 2022 Commonwealth Games and competed in the women's tandem event. She finished third in the competition however, no bronze medal was awarded as the minimum five entries did not compete, after a late withdrawal from the fifth entered team.[3] This prompted Unwin to protest against the decision to not award her a bronze medal despite finishing third.[4] She along with her pilot Georgia Holt attempted to stand behind the podium ceremony with the flag of England before being escorted/moved by a security staff member and as a result Unwin was subsequently fined for breaching the code of conduct and she left the scene with tears.[5][6]
On 22 July 2024 it was announced that Unwin had been selected for the British team for the 2024 Paralympic Games in Paris, her second Games.[7] She competed in both road and track cycling disciplines and medalled in all four of her events, all piloted by Jenny Holl. The first of these medals, a bronze, came on 30 August in the women's 1000 m time trial B. A second medal, her first Paralympic gold, came two days later in the women's 3000 m pursuit B. In the road time trial B on 4 September she claimed silver, beating fellow British pairing Lora Fachie and Corrine Hall, who won bronze. Unwin won a second gold medal of the Games in the women's road race B.[8]