During his early years Muller was a standout pitcher for the Which Wich Grinders and attended Jesuit College Preparatory School in Dallas, Texas.
[5] He made his professional debut in 2018, splitting time between the rookie-level Gulf Coast Rays and Low-A Hudson Valley Renegades.
[8] He instead played for the Sugar Land Lightning Sloths of the Constellation Energy League, where he logged a 5.63 ERA with 9 strikeouts and 2 saves in 7 appearances.
[10] He spent the 2022 season with the Triple-A Durham Bulls, making 51 appearances and registering a 5–3 record and 4.91 ERA with 75 strikeouts and 2 saves in 58.2 innings pitched.
[11] Muller was assigned to Triple-A Durham to begin the 2023 season, where he made 14 appearances and posted a 3.71 ERA with 19 strikeouts and 1 save in 17.0 innings pitched.