Mirocha began karting in 2001 in Koszalin, Poland. He finished third in the German Karting Championship Junior class in 2005.
Mirocha made his car racing debut in the 2007 Formula BMW ADAC championship, competing under the ADAC Berlin-Brandenburg banner with Mucke Motorsport. He finished eighth in the championship and third in the Rookie Cup, taking one podium at EuroSpeedway Lausitz. He also appeared at the 2007 Formula BMW World Final with Josef Kaufmann Racing, finishing 22nd.
In 2008 Mirocha stepped up to the ATS Formel 3 Cup with Josef Kaufmann Racing, recording four podium finishes and placing sixth overall in the standings. For 2009 he moved to HBR Motorsport in the Formula 3 Euro Series but sustained a shoulder injury; he failed to start either race at the Zandvoort round and ended the season without championship points.
Mirocha contested seven of the twenty rounds in the 2010 Formula Renault 2.0 NEC season with SL Formula Racing. Despite the partial campaign, he won the final race of the season at the Nürburgring — taking pole position and fastest lap in the same weekend — and finished ninth in the championship, the third-best-placed driver among those who had not competed in all rounds. He also made two guest appearances in the 2010 Eurocup Formula Renault at Hockenheim, finishing ninth and eleventh, though he was ineligible for championship points.
Mirocha joined Ocean Racing Technology in the GP2 Series for 2011, partnered with Johnny Cecotto Jr. A left shoulder injury suffered at Silverstone prevented him from starting either race at that round. He was subsequently replaced by Brendon Hartley for the remaining rounds after fourteen races. Despite scoring no championship points Mirocha was classified 22nd in the final standings, the highest-placed driver without a point — a reflection of the reliability and pace shown despite the injury disruption.
In 2012 Mirocha competed in the FIA Formula Two Championship with Motorsport Vision, driving a Williams JPH1B powered by a Mountune Audi engine. The season was his strongest in single-seaters. He took his maiden victory in the category at Brands Hatch and added five further podium finishes across the sixteen-race season. He also set the pole position at the Hungaroring round. He accumulated 159.5 championship points and finished sixth overall — a strong debut season in a spec series known for close competition.
Following the Formula Two season, Mirocha stepped back from the top of the European single-seater ladder. He returned to competition in 2022, contesting the Indian Racing League with the Goa Aces franchise in a Wolf GB08 Thunder, scoring two podiums from four starts to finish twelfth overall. In 2025 he entered the Lamborghini Super Trofeo Europe Pro-Am category with GT3 Poland, starting at the Catalunya round before retiring from the race.