Tamaș started his career in lower divisions. In the summer of 2002 he transferred to Dinamo București who he spent a year with before earning a move to Turkish team Galatasaray where he spent a season-and-a-half before being linked with a move to the Russian Premier League.

Tamaș secured a move to Spartak Moscow in January 2004, but returned to Dinamo București in summer 2004 on a season-and-a-half loan, returning to Spartak in January 2006. Tamaș again moved out on loan to Celta de Vigo of Spain for the duration of the 2006–07 season.

He joined AJ Auxerre in France at the start of the 2007–08 season. After one year there he again joined Dinamo București, this time on a season-long loan. On 12 July 2009, he extended his loan for another season, and was also elected captain by his teammates.

His loan to Dinamo was cut short in December 2009, and on 1 January 2010, Tamaș signed for West Bromwich Albion on loan until the end of the season. He made his debut on 8 January in a 1–3 loss to Nottingham Forest.[5] He scored his first goal for the Football League Championship club against Reading on 27 March 2010.[6] On 19 May 2010, Tamaș signed permanently at The Hawthorns for an undisclosed fee on a three-year contract, plus a further year's option in the club's favour.[7] On 11 September 2011, in a match against Norwich City, he elbowed James Vaughan in the face inside his own penalty area. The referee gave no penalty and let the play continue, but he was given a three-match ban for violent conduct after the match.[8] He ended his contract with WBA by mutual consent, in September 2013.[9]

On 17 January 2014, he returned to England by signing for Doncaster Rovers.[10] Upon the expiry of his contract, Tamaș signed for Watford on a one-year contract effective from 1 July.[11]

After suffering a cruciate knee ligament injury in September 2014, Tamaș cancelled his contract with Watford in January 2015.[12] On 15 January 2015, he signed a two-year contract with FCSB, the great historic rival of his former club Dinamo București.[13]

On 26 August 2015, Tamaș joined Championship side Cardiff City on a one-year deal, with a further option to a second year.[14][15] During the first half of the season, Tamaș only appeared for the development squad and wasn't involved in the first team at all from November, resulting in frustration and claiming he wanted to leave Welsh capital.[16] He eventually made his first team debut in a FA Cup loss to Shrewsbury Town on 10 January.[17] On 1 February 2016, his contract was terminated by mutual agreement.[18] Tamas then returned to FCSB, albeit on a lower wage. His deal at FCSB was offered by the club's ow