Hallmann graduated from Akademia Marynarki Wojennej and is currently an officer of the Navy, with the rank of Secondary Lieutenant.
Hallmann had made his professional debut at "Beast of the East" event in his hometown, Gdynia, on November 14, 2009, when he defeated Krzysztof Adaszak.
He won Casino Fight Night 2011 tournament in Erfurt, as well as World Freefight Challenge and Celtic Gladiator lightweight championship titles.
Hallmann faced Al Iaquinta on October 26, 2013 at UFC Fight Night: Machida vs. Munoz.
[7] Hallman faced promotional newcomer Magomed Mustafaev on June 20, 2015 at UFC Fight Night 69.
[8] He lost the fight via TKO in the second round, after the referee stopped the contest on the advice of the doctor due to a large cut over Hallman's left eye.