Van der Merwe's roots lie in Potchefstroom. He was born there, matriculated at Potchefstroom Gymnasium and studied at the North-West University.
Gideon Johann van der Merwe was born on 27 January 1995 in Potchefstroom - the year Francois Pienaar's team won the World Cup.
As a product of Potchefstroom Gym, Van der Merwe was called up to represent the Leopards at the youth level in 2013 at the Under-18 Craven Week in Polokwane.
After finishing high school, Van der Merwe joined the Pukke of the North West University in Potchefstroom.
In 2015 and 2016, he made his mark for Pukke's Young Guns.
In 2016 and 2017, Gideon played for the Leopards' u.21 team and the Pukke's Varsity Cup team, and he made his debut for the Leopards in the SuperSport series.
In 2016 Gideon played for the Pukke in the 2016 Varsity Cup Competition. Two of Van der Merwe's Cheetah teammates - Jeandré Rudolph (flank) and the Namibian international Louis van der Westhuizen (hooker), were his teammates in that Pukke side that won the Varsity Cup in 2016. Rudolph was captain of that Pukke side.
Van der Merwe made his first-class debut on 25 August 2017 for the Leopards against South West Districts at Potchefstroom, scoring one of the Leopard's five tries in a drawn match, 42-42. Gideon played in 21 games for the Leopards, scoring eight tries. Rudolph and Van der Westhuizen joined Van der Merwe as teammates in the Leopards' Currie Cup 1St Division campaign.
Van der Merwe made his Currie Cup debut for Griquas on 12 July 2019, starting their opening match of the 2019 season against the Sharks. He played in 34 games for the Griquas scoring 12 tries.
Van der Merwe, in November 2019, made his way to the Free State. In November 2021, Van der Merwe signed a deal with the Cheetahs. He made his Cheetah debut on 13 November 2021 against Western Province XV in Bloemfontein, scoring his first eight tries in his 14 Cheetah matches.