Koman was born in Uzhhorod, Zakarpattia Oblast, Ukrainian SSR, Soviet Union. When he was a child, in 1991, his family moved to Szombathely where he played his first games for the local football team Haladás and made his debut on NB2 league at just 15 years. His father, Volodymyr Koman was also a football player. Koman played 25 matches and scored 3 goals in the 2004–05 season of the Hungarian National Championship II.
Koman made his Serie A debut on 7 April 2007 in a home match against Torino directly from the starting lineup, and gave the assist for the only goal in the game, scored by Emiliano Bonazzoli. He then led Sampdoria to win the 2007–08 Campionato Primavera title, and also took part at the 2008 UEFA European Under-19 Football Championship captaining the Hungary U-19 team.
He spent the 2008–09 season on loan to Avellino. Koman played 28 matches and scoed four goals in the Serie B squad of US Avellino. Koman had been loaned out to A.S. Bari for the 2009–10 season. He scored his first Serie A goal against Palermo in a 4–2 win on 30 January 2010, thus making him the first Hungarian player to score in the Italian top flight in the last 15 years. He ended up the season with two goals in 16 appearances. He re-joined Sampdoria for the 2010–11 season. In the 2010–11 season of the Serie A Koman became a permanent member of the Genovese squad. In the 2010–11 UEFA Europa League, Koman assisted a goal against PSV Eindhoven. Koman scored his first goal against Metalist Kharkiv in the 32nd minute of match in the Europa League. Koman was appointed as a captain against Debreceni VSC in the last round of the 2010–11 UEFA Europa League season.
On 31 January 2012 Koman was transferred to AS Monaco FC on a four-and-a-half deal. Koman's contract with Sampdoria was due to expire in May 2012. On 15 April Koman was interviewed after the victory against Metz. He iterated that he is expecting his first goal and he enjoys playing in the Ligue 2. However, after playing 17 matches he left the club for FC Krasnodar in order to play in the Russian first division.
In June 2012 Koman signed a contract with Russian Premier League club FC Krasnodar. On 23 July 2012 Koman debuted in the Russian Premier League against Rubin Kazan with 2–1 victory. He scored his first goal against FC Volga Nizhny Novgorod at an eventual 1–1 away draw. Koman was released by Krasnodar on 2 July 2014.
On 1 July 2014, FC Krasnodar and Koman mutually terminated their contract. Koman became a free agent.
In August 2014, the Hungarian League club Diósgyőr wanted to sign Koman, but finally he rejected the offer of the Miskolc-based club. Koman's manager Bálint Kovács confirmed to Nemzeti Sport that the Belgian Pro League club FC Bruges showed interest in signing Koman in September 2014.
On 12 November 2014, Koman was cited by the famous American digital media company Bleacher Report as one of the most notable free agent available in the 2014–15 season along with Víctor Valdés and Simão Sabrosa.
Due to lack of playing minutes, in the summer transfer window, Koman was loaned out to fellow league club, FC Ural, and made his debut in his new team, on 16 September 2013, against Dynamo Moscow, where he played the full match.
On 15 May 2014, Koman scored his first goal in the 2013–14 Russian Premier League season on the 30th match day against FC Volga Nizhny Novgorod in the 45th minute. The match was won by FC Ural.
On 4 February 2015, Koman was signed by Hungarian League club Diósgyőr. On 1 August 2015, Koman scored his first goal for Diósgyőri VTK in the 2015–16 Nemzeti Bajnokság I match in a 2–1 defeat against title-holders Videoton FC at the DVTK Stadion, Miskolc. He scored the goal from a penalty kick in the 9th minute. On 12 December 2015, he scored his second goal in the 2015–16 Nemzeti Bajnokság I season against Békéscsaba 1912 Előre at the DVTK Stadion, Miskolc, in the 61st minute.
According to the Croatian SportCom.hr, Croatian First Football League club HNK Rijeka showed interest in signing Koman. The Croatian club is looking for a player which replace Moisés Lima Magalhães who left HNK Rijeka for Série A club Sociedade Esportiva Palmeiras.
Koman was part of the Hungarian national team, which won the bronze medal on the 2009 FIFA U-20 World Cup. He scored five goals in six matches which made him second on the top goalscorers' list behind Dominic Adiyiah of Ghana. He has been recently called up to the Hungary by national coach Erwin Koeman for the friendlies against Germany and The Netherlands in late May and early June 2010. He made his international debut for Hungary against Germany on 29 May 2010. Koman scored his first international goal against Moldova in the Szusza Ferenc Stadium in the Euro 2012 qualifier. Finally, Hungary beat Moldova 2–1 on home turf. Koman's scored his second goal against San Marino in the Puskás Ferenc Stadium in the Euro 2012 qualifier. On 7 June 2011, Koman scored his third goal in the UEFA Euro 2012 qualifier match against San Marino. Hungary won the match 3–0 in San Marino. Koman scored the first goal of the four against Iceland at the Puskás Ferenc Stadium. The match finished 4–0 to Hungary. On 7 September, Hungary started the FIFA world cup 2014 qualifying with a 5-0 win in Andorra, Koman scored the fifth Hungarian goal in the 82nd minute. On 16 October 2012, Hungary battle back to beat Turkey at home 3-1. Koman scored the equalizer which gave the courage for the national team to beat Turkey. On 10 September 2013, Koman gave two assists, one for his ex-U-21 teammate Németh who scored his first goal wearing the national Team's shirt and one for Tamás Hajnal, in a 5-1 victory over Estonia in the 2014 FIFA World Cup qualification match at the Puskás Ferenc Stadium.As of 24 November 2015
SampdoriaTrofeo Giacinto Facchetti: 2007–08
HungaryUEFA European Under-17 Football Championship:
Final tournament: 2006
UEFA European Under-19 Football Championship:
FIFA U-20 World Cup:
Third place: 2009
2009 FIFA U-20 World Cup Silver Shoe
In June 2014, Koman married to his Russian girlfriend Zarina at the Four Seasons Hotel in Budapest.