[2] Mulder made his first-class cricket debut at The Wanderers for Highveld Lions against Cape Cobras in the 2016–17 Sunfoil Series in October 2016 whist still at school.
[9][10] He played in three matches for Kent before being recalled to the South African team, ahead of their international schedule.
[14] In November 2021, Mulder was signed by Leicestershire County Cricket Club to play in England during the 2022 season.
[15] In July 2022, in the County Championship, Mulder scored his maiden double century in first-class cricket with 235 not out.
[21] In February, Mulder was once again named in South Africa's squad, this time for their Test series against Sri Lanka.