Tomas began his career with Sigma Olomouc but found it difficult to make the breakthrough at the Czech club making only one competitive first team appearance for the club.
His talent, however, was undeniably and he represented the Czech Republic at various youth levels representing the Under 17s, 18s, 19s and 21s with distinction.
In 2007 he moved to Hamilton Accies, originally on loan, and was part of the side which won promotion to the SPL in the 2007/08 season. He stayed with the club as they battled to stay in the top flight of Scottish football, a battle which was successful for two years before the side suffered relegation.
Tomas stayed with the club despite their demotion to the First Division but in early 2012, having made over 150 appearances for the Lanarkshire side, he left the club.
Tomas moved onto CSKA Sofia where he spent two seasons before moving to Greek Super League club Ergotelis in June 2014, signing a two year deal. After a few months with the Greek club, they fell into financial problems and Tomas elected to leave the club returning to Scotland. He signed a short term contract with Hibernian in January 2015 but failed to displace Mark Oxley between the posts.
He signed a one year deal with Thistle at the start of June and will spend 2015/16 with the club in the Scottish Premiership.