Career
He started out playing for his home town club KSZO Ostrowiec Świętokrzyski. Wisła Krakow and loans
He moved to 1. Football Club Kaiserslautern in Germany in 2003 and then on to Southampton Football Club where he played the 2005-2006 season on a year-long loan and was recalled to the Polish national team
He scored once in the league for Southampton, in a 1–1 draw with Hull City.
After being on loan at A.C. (before Christ) Chievo Verona, Kosowski returned to Wisła Krakow and played very well for the first half of the season as the player with most assists in the first half of the league campaign after setting up nine goals in 13 games. However on 14 January 2008, Wisła Krakow and Kosowski mutually voided the remainder of his contract as a result of not coming to a compromise on a new deal.
Cádiz CF
Kosowski signed a two and a half year contract with Spanish second division team Cádiz CF on 25 January 2008. Cadiz finished 20th in Segunda Division (2007-2008) and were relegated to Segunda Division B.
APOEL Nicosia
On 7 July 2008, he was transferred to APOEL from Cádiz CF and signed a two-year contract.
He stated that his participation with APOEL in the Union of European Football Associations Champions League was one of the most important moments in his career.
Apollon Limassol
On 31 May 2010, he signed a two-year contract with Apollon Limassol but at the end of the season his contract was mutually terminated. GKS Bełchatów
In July 2011, he joined GKS Bełchatów on a one-year contract. Kosowski was capped 52 times for Poland, scoring four goals.
He was selected to the 23-men national squad for the 2006 Fédération internationale de football association World Cup finals held in Germany, but he played only about fifteen minutes against Ecuador.
International goals.