Kozin made her professional debut on 24 September 2016, scoring a four-round unanimous decision (UD) victory over Ina Milohanic at the Tabor Arena in Maribor, Slovenia.

[7] She moved up to super-middleweight for her next bout, fighting to a split draw against Irais Hernandez with the vacant WBC Silver and WBF female titles up for grabs on 8 September 2018 at Arena Zagreb in Croatia.

Kozin defeated Turunen via UD to become the WBF female and WIBA champion in two weight classes, simultaneously, with the judges' scorecards reading 99–91, 98–92, and 97–93.

[12] On 24 June 2023, Ema Kozin successfully defended her title of the world champion in the WBF super welterweight category by defeating Timea Belik from Hungary in ten 2-minute rounds in Altdorf, Germany.

[citation needed] Kozin defeated Scotland's Hannah Rankin for the vacant WBC and WBO female super-welterweight World titles in Manchester on 18 November 2023 winning the contest by split decision.