[5][6] Mielnicki fought against Marklin Bailey on the undercard of Deontay Wilder vs. Luis Ortiz II on November 23, 2019.
[7][8] Mielnicki was taken the full distance for the first time in his professional career when he fought against Preston Wilson on January 18, 2020.
[9] Mielnicki's fifth bout as a professional was on the undercard of Deontay Wilder vs. Tyson Fury II against Corey Champion on February 22, 2020.
Champion recovered from the knockdown, but despite this, Mielnicki proceeded to dominate the remainder of the fight and won via wide unanimous decision.
[12] Mielnicki was taken the full fight distance for the third time as a professional when he fought Steven Pulluaim on December 5, 2020.
Mielnicki secured victory in the third round after he landed a barrage of punches on Lopez which forced the referee to end the bout.
It was announced on the day of the weigh-in that Martin would be unable to make the contracted weight, so Mielnicki would instead fight Noah Kidd.
[28] Mielnicki was scheduled to face Laszlo Toth in a 10-round super welterweight bout in Albuquerque, NM on August 10, 2024.
[30][31] Mielnicki is scheduled to face Daniel Buciuc in a 10-round super welterweight bout at The Theater at Madison Square Garden in New York on September 27, 2024.