Jemelka started his professional career with Sigma Olomouc, spending six years with the club including a season where he played on loan in Belgium for OH Leuven.

[6] Jemelka joined Viktoria Plzeň in August 2022, signing a three-year contract with the club.

[8] On 11 November 2020, Jemelka debuted for the Czech senior squad in a friendly match against Germany.

[9] In March 2021, he was called up for the 2022 FIFA World Cup qualification to replace the injured Tomáš Kalas, but felt ill and had to stay at home for the match against Estonia national football team.

[10] Jemelka also was not included in the Czech Republic's UEFA Euro 2020 squad due to another health issue.