He made his PDC European Tour debut in the 2019 Dutch Darts Masters, but lost 6–1 to Glen Durrant.

Merkx also made his first final on the BDO/WDF circuit that year, losing 6-3 to Martin Barratt at the Lithuania Open.

Merkx became a WDF Tour regular in 2022, winning ranking titles in Lithuania and Switzerland.

He qualified for the 2023 WDF World Championships, winning his first game against Arjan Konterman before losing to Dennis Nilsson in the Last 16.

Merkx won a third WDF title in January 2024 when he triumphed at the Romanian Open.