Career
Hearts
Mrowiec joined Hearts on loan from FBK Kaunas in 2008 as a holding midfielder, he made his debut against Falkirk in a 2–1 away defeat. Arka Gdynia
In July 2009 he moved to Arka Gdynia in the Polish Ekstraklasa on a one-year loan. Return To Hearts
Mrowiec returned to Hearts for a trial spell in 2010 and he subsequently signed a three-year contract.
He left Hearts in May 2012 having not being offered a new contract.
Germany
On the 18 May 2012, he joined German side RB Leipzig on two-year contract. He was released by the club without making a league appearance and signed for Chemnitzer Football Club.