| Club: | Union Berlin |
| Season: | 2020–21 |
| Chrtitle: | Chairman |
| Chairman: | Dirk Zingler |
| Manager: | Urs Fischer |
| Stadium: | Stadion An der Alten Försterei |
| League: | Bundesliga |
| League Result: | 7th |
| Cup1: | DFB-Pokal |
| Cup1 Result: | Second round |
| League Topscorer: | Max Kruse (11) |
| Season Topscorer: | Max Kruse (11) |
| Largest Win: | Union Berlin 5–0 Arminia Bielefeld |
| Largest Loss: | Eintracht Frankfurt 5–2 Union Berlin VfL Wolfsburg 3–0 Union Berlin |
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| Prevseason: | 2019–20 |
| Nextseason: | 2021–22 |
The 2020–21 1. FC Union Berlin season was the club's 56th season in existence and the second consecutive season in the top flight of German football, the Bundesliga. They also participated in the DFB-Pokal. The season covered the period from 1 July 2020 to 30 June 2021.
| width=170 | Player | width=170 | From | width=90 | width=70 data-sort-type="number" | in € | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| FW | Marius Bülter | 1. FC Magdeburg | Transfer | Summer | 2022 | 1,400,000 | ||||
| FW | Cedric Teuchert | Schalke 04 | Transfer | Summer | 2022 | |||||
| FW | Max Kruse |  Fenerbahçe | End of contract | Summer | ? | – | ||||
| DF | Niko Gießelmann | Fortuna Düsseldorf | End of contract | Summer | 2021 | – | ||||
| MF | Sebastian Griesbeck | 1. FC Heidenheim | End of contract | Summer | 2022 | – | ||||
| DF | Robin Knoche | VfL Wolfsburg | End of contract | Summer | 2022 | – | ||||
| GK | Andreas Luthe | FC Augsburg | End of contract | Summer | 2022 | – | ||||
| FW |  Taiwo Awoniyi | Liverpool | Loan | Summer | 2021 | |||||
| GK | Loris Karius | Liverpool | Loan | Summer | 2021 | |||||
| FW |  Joel Pohjanpalo | Bayer Leverkusen | Loan | Summer | 2021 | |||||
| MF |  Keita Endo | Yokohama Marinos | Loan | Summer | 2021 | 300,000 | ||||
| DF | Nico Schlotterbeck | SC Freiburg | Loan | Summer | 2021 | 200,000 | ||||
| MF | Leon Dajaku | Bayern Munich | Loan | Winter | 2021 |
| width=170 | Player | width=170 | To | width=90 | width=70 data-sort-type="number" | in € | |||
|---|---|---|---|---|---|---|---|---|---|
| FW |  Sebastian Andersson | 1. FC Köln | Transfer | Summer | 6,500,000 | ||||
| DF |  Neven Subotić | Denizlispor | Transfer | Summer | |||||
| MF | Lars Dietz | Würzburger Kickers | Transfer | Summer | |||||
| MF |  Florian Flecker | Würzburger Kickers | Transfer | Summer | |||||
| MF | Julius Kade | Dynamo Dresden | Transfer | Summer | |||||
| MF | Joshua Mees | Holstein Kiel | Transfer | Summer | |||||
| DF | Lennard Maloney | Borussia Dortmund II | Transfer | Summer | |||||
| MF | Berkan Taz | SC Verl | Transfer | Summer | |||||
| GK |  Rafal Gikiewicz | FC Augsburg | End of contract | Summer | – | ||||
| MF | Felix Kroos | Eintracht Braunschweig | End of contract | Summer | – | ||||
| GK | Leo Oppermann | Hamburger SV II | End of contract | Summer | – | ||||
| FW | Sebastian Polter | Fortuna Sittard | End of contract | Summer | – | ||||
| DF | Ken Reichel | VfL Osnabrück | End of contract | Summer | – | ||||
| MF | Manuel Schmiedebach | Free agent | End of contract | Summer | – | ||||
| DF | Michael Parensen | – | Retired | Summer | – | ||||
| MF | Suleiman Abdullahi | Eintracht Braunschweig | Loan | Summer | – | ||||
| MF | Laurenz Dehl | Hallescher FC | Loan | Summer | – |
See main article: 2020–21 Bundesliga.
The league fixtures were announced on 7 August 2020.[1]
See main article: 2020–21 DFB-Pokal.
|-! colspan=14 style=background:#dcdcdc; text-align:center| Goalkeepers|-! colspan=14 style=background:#dcdcdc; text-align:center| Defenders|-! colspan=14 style=background:#dcdcdc; text-align:center| Midfielders|-! colspan=14 style=background:#dcdcdc; text-align:center| Forwards|-! colspan=14 style=background:#dcdcdc; text-align:center| Players transferred out during the season|-