Nogometni Klub Osijek, usually known by the more simple name of Osijek, was first established in February 1947. However, its roots can be traced back further, to the creation of NK Udarnik under Yugoslavia's communist regime in 1945. NK Udarnik later merged with several clubs, but their merger with NK Bratstvo in 1947 is considered the present side's birth date. Their main rivals are Cibalia, with whom they contest the Slavonian Derby.
After missing out on promotion several times, Osijek gained entry to the Yugoslav First Division for the first time in 1953. However, their stay in the league was fairly short-lived and a few years later, they were relegated. As a result, the club spent much of the following decades attempting to return to the top flight.
Since the establishment of Croatia's own independent football league, Osijek have grown in stature as a club. They were a founding member of the top division, the Prva HNL, in 1992 and have never been relegated from it. On several occasions, the team have competed near the top of the league, achieving a number of third place finishes. In 1998–99, Osijek lifted their first major trophy, the Croatian Cup, and in 2011-12 they were runners up in the competition. The side have also competed in several continental competitions, with their best performance coming in the 2000–01 UEFA Cup, where they reached the third round.
Amongst the team's most notable former players are Croatian intertationals like Robert Špehar, Stanko Bubalo and Petar Krpan, as well as Ivan Miličević and Vedran Nikšić.
Osijek play their home matches at the Stadion Gradski vrt, which opened in 1980 and underwent renovations in 2005. It currently holds a maximum of 22,050 supporters, although the record attendance was set at 40,000 spectators for a match against Dinamo Zagreb in 1982.