During the Cold War, Union was based in East Berlin, joining the German league structure upon the reunification of the city and country in 1990.

Early on, the team was nicknamed "Schlosserjungs" (English: metalworker-boys) because of their then all blue kit, reminiscent of the typical work clothing worn in the factories of the industrial Oberschöneweide district.

After World War II, occupying Allied authorities ordered the dissolution of all organizations in Germany, including sports and football associations.

A new sport community called SG Oberschöneweide was formed in late 1945 and it played in the City League organized immediately after the war which had four regional departments.

The team did not qualify to the newly created Oberliga Berlin (I) in 1946 after a poor season, but was promoted in 1947, won the division title right away and regained club status as SG Union Oberschöneweide during 1948–49.

However, escalating Cold War tensions led Soviet authorities to refuse the team permission to travel to take part.

[citation needed] The western team was a strong side until the construction of the Berlin Wall in 1961, drawing huge crowds to matches in the Olympiastadion.

[16] The club was founded in a ceremony in the clubhouse of VEB Transformatorenwerk Oberschöneheide "Karl Liebknecht" (TRO) in Oberschöneweide on 20 January 1966.

[23] The first club president was the general director of VVB Hochspannungsgeräte und Kabel, Werner Otto, and his deputy was the SED Second Secretary in East Berlin, Hans Wagner.

They were finally successful in 2000–01, under Bulgarian manager Georgi Vasilev, easily winning the Regionalliga Nord (III) and moving up a division to become the city's second most popular side.

that club president Dirk Zingler had been a member of the Felix Dzerzhinsky Guards Regiment for three years during his military service.

[34] Zingler had also been a member of the Socialist Unity Party (SED) and leader in the Free German Youth (FDJ) at the time.

[39] The team remained in the second tier until the 2018–19 season, when they secured a first promotion to the Bundesliga after defeating VfB Stuttgart in the relegation play-offs.

[48] In the 2022–23 season, Union Berlin qualified for the Champions League group stage for the first time in its history, after a 1–0 home win against Werder Bremen on the final matchday.

[49] In the 2023–24 season, the club experienced a bad start including 14 winless competitive matches in a row, hence they decided to separate with coach Urs Fischer by "mutual agreement".

FC Union Berlin) had to find a new home ground as its former pitch had been built over by developers with residential buildings.The club moved a little further away from the city to the north-western part of the borough of Köpenick.

In the middle of 2008, the club decided to finally modernise the stadium, the Stadion An der Alten Försterei (Old Forester's House).

Inside the stadium an array of outside beer kiosks and open air grills serving bratwurst and pork steaks at the back of the stand provide the culinary staples.

In 2014, the club came up with the idea of inviting their fans to take their own sofas to the ground for the whole of the World Cup, to enjoy the televised matches in the company of fellow supporters.

These nicknames evolved from the earlier sobriquet Schlosserjungs (metalworker boys), a reference to the blue kit the Union played in, as it was reminiscent of the overalls worn by local workers.

[72] Wildz is the sister brand to Wheelz, a platform that features The Hoff, an entertainment figure who also enjoys cult status in Germany.

FC Union Berlin was known for a rivalry with BFC Dynamo, which was reputedly affiliated with the powerful state security service of East Germany (Stasi).

Union, on the other hand, was supported by the regional district management of the ruling SED party and sponsored by local state-owned enterprises.

[73] Between 1979 and 1988, BFC Dynamo won ten consecutive East German league titles, with popular allegations of sporting misconduct helping to fuel the rivalry, and clashes between both sets of fans occurred.

[74] BFC Dynamo was seen as the supreme representative of the security agencies, with advantages in the recruitment of players and financial support, as well as the political clout of Erich Mielke.

Fans of both clubs paid for admission in East and West Germany's respective currencies, and sang songs of German reunification, as Hertha won 2–1.

Over twenty years later, on 17 September 2010, the duo faced each other for the first time in a competitive meeting, at the Stadion An der Alten Försterei, drawing 1–1 in the 2.

[93] On 2 November 2019, Union Berlin faced Hertha at the Stadion An der Alten Försterei, in the first meeting between the clubs in German football's top flight.

[94] Union Berlin also holds rivalries with Hansa Rostock,[96] Dynamo Dresden,[97] and Magdeburg, dating to when the teams competed in the DDR-Oberliga.

Fans drink Glühwein (mulled wine), wave candles around, light flares and sing a combination of Christmas carols and football chants.