Born in Pljevlja, SR Montenegro, SFR Yugoslavia, Tomašević arrived in Portugal with CD Nacional aged 18.

In 2009, he was called up to the first team by Manuel Machado, making his first division debut in a 1–1 home draw against Sporting CP, on 15 August 2009, and also totalled 17 minutes combined in the Madeiran club's historical UEFA Europa League 5–4 aggregate win against Zenit Saint Petersburg.

[3] After leaving Astana at the end of the 2021 season, Tomašević went on to sign a one-year contract with Tobol on 27 January 2022.

[6][7] In late August 2009, Tomašević was first called to the Montenegro under-21 squad, for a 2011 European Championship qualifier against Sweden, in which his country lost 2–0 at home.

In 2014, he scored his first international goal for Montenegro against Moldova in a 2016 European Championship qualification match.