Hewett was born with a congenital heart defect that required surgery at six months, and suffered from Legg–Calvé–Perthes disease, a condition that inhibits blood flow from the pelvis to the hip joint.

[4] In July 2016 Hewett won the 2016 Wimbledon Championships – Wheelchair men's doubles, alongside Gordon Reid, coming back from a set down to win against the French pair Stéphane Houdet and Nicolas Peifer.

In May 2017 Hewett won his first Grand Slam in singles at the French Open, beating Gustavo Fernández of Argentina in three sets, despite losing the first to love.

In July 2017, in a repeat of the final a year earlier, Hewett won the 2017 Wimbledon Championships – Wheelchair men's doubles, alongside Reid, winning in three sets against Houdet and Peifer.

[8][9] After winning a silver medal in the men's doubles with Reid at the 2020 Summer Paralympics[10] and losing the bronze medal singles match to Reid, world number 2[10] Hewett spoke about his Paralympic future being "out of his hands",[10] due to a review into whether his disability is severe enough to qualify him to play in a wheelchair under the 2019 revision of International Tennis Federation rules.

[14] Hewett and Reid won a fifth straight French Open in June with a 6-1 6-4 victory over second-seeded Japanese duo Takuya Miki and Tokito Oda in the final.

[15] At the 2024 Wimbledon Championships, Hewett defeated Martín de la Puente in the final, 6–2, 6–3, to complete the singles career Grand Slam.