Hashemian started his professional football career with Pas Tehran in his homeland. He arrived in Germany for the 1999–2000 season to play for Hamburger SV. Although playing alongside his fellow Iranian international Mehdi Mahdavikia, he had just 12 appearances, so he left the club for VfL Bochum to show his real ability. He had three good seasons with Bochum, scoring 34 goals in 87 appearances. During his last season there he scored 16 goals, helping Bochum to finish fifth in the Bundesliga and qualify for the 2004–05 UEFA Cup. This prompted Bayern Munich to grant him in a €2M contract, hence giving him the chance to follow in the footsteps of Ali Daei. After one season with Bayern Munich, he joined Hannover 96 where he has been playing since season 2005–06. On 23 April 2008, VfL Bochum officials announced that he would return to their club in the season 2008–09. Hashemian signed a two year contract with an option for one extra year. He scored only one goal for the team and was benched most of the times in his first season. On 30 December 2010, Hashemian signed a deal with Iran Pro League side Persepolis. Where he was able to win the Hazfi Cup. On 19 July 2011, he extended his contract with the Iranian powerhouse Persepolis for another year. On 20 May 2012, It was announced that he will be leaving the club at the end of the season. On 21 July 2012, on his 36th birthday, he announced his retirement from soccer.
On 26 October 2012, he was appointed as coach of Regionalliga side SV Halstenbek-Rellingen in the Hamburg Oberliga but after a successful run with the team, he announced his resignation at the end of the season.