Union Berlin baru promosi ke Bundesliga pada musim 2018/2019. Musim lalu, mereka berhasil bertahan dengan berada di peringkat ke-11. Di awal musim ini, Union Berlin tampil bagus. Hingga pekan ketujuh, mereka berada di peringkat kelima.
Daftar Nama Pemain Union Berlin Musim 2020/2021
| No. | Pos. | Player |
| 1 | GK | Andreas Luthe |
| 4 | DF | Nico Schlotterbeck |
| 5 | DF | Marvin Friedrich |
| 6 | MF | Julian Ryerson |
| 7 | MF | Akaki Gogia |
| 9 | FW | Joel Pohjanpalo |
| 10 | FW | Max Kruse |
| 11 | FW | Anthony Ujah |
| 12 | GK | Jakob Busk |
| 14 | FW | Taiwo Awoniyi |
| 15 | FW | Marius Bülter |
| 16 | MF | Tim Maciejewski |
| 18 | MF | Keita Endo |
| 19 | DF | Florian Hübner |
| 20 | GK | Loris Karius |
| 21 | MF | Grischa Prömel |
| 23 | DF | Niko Gießelmann |
| 25 | DF | Christopher Lenz |
| 27 | FW | Sheraldo Becker |
| 28 | DF | Christopher Trimmel (Captain) |
| 30 | MF | Robert Andrich |
| 31 | DF | Robin Knoche |
| 32 | FW | Marcus Ingvartsen |
| 33 | MF | Sebastian Griesbeck |
| 34 | MF | Christian Gentner |
| 35 | GK | Lennart Moser |
| 36 | FW | Cedric Teuchert |
Daftar Nama Pemain Baru Union Berlin Musim 2020/2021
| Pos | Nama | Dari | Ket |
| FW | Marius Bülter | 1. FC Magdeburg | 1,400,000 |
| FW | Cedric Teuchert | Schalke 04 | Gratis |
| FW | Max Kruse | Fenerbahçe | |
| DF | Niko Gießelmann | Fortuna Düsseldorf | |
| MF | Sebastian Griesbeck | 1. FC Heidenheim | |
| DF | Robin Knoche | VfL Wolfsburg | |
| GK | Andreas Luthe | FC Augsburg | |
| FW | Taiwo Awoniyi | Liverpool | Pinjaman |
| GK | Loris Karius | Liverpool | Pinjaman |
| FW | Joel Pohjanpalo | Bayer Leverkusen | Pinjaman |
| MF | Keita Endo | Yokohama Marinos | Pinjaman |
| DF | Nico Schlotterbeck | SC Freiburg | Pinjaman |
Daftar Nama Pemain yang Keluar dari Union Berlin Musim 2020/2021
| Pos | Nama | Ke | Ket |
| FW | Sebastian Andersson | 1. FC Köln | 6,500,000 |
| DF | Neven Subotić | Denizlispor | Gratis |
| MF | Lars Dietz | Würzburger Kickers | Gratis |
| MF | Florian Flecker | Würzburger Kickers | Gratis |
| MF | Julius Kade | Dynamo Dresden | Gratis |
| MF | Joshua Mees | Holstein Kiel | Gratis |
| DF | Lennard Maloney | Borussia Dortmund II | Gratis |
| MF | Berkan Taz | SC Verl | Gratis |
| GK | Rafal Gikiewicz | FC Augsburg | Kontrak Habis |
| MF | Felix Kroos | Eintracht Braunschweig | Kontrak Habis |
| GK | Leo Oppermann | Hamburger SV II | Kontrak Habis |
| FW | Sebastian Polter | Fortuna Sittard | Kontrak Habis |
| DF | Ken Reichel | VfL Osnabrück | Kontrak Habis |
| MF | Manuel Schmiedebach | Bebas Transfer | Kontrak Habis |
| DF | Michael Parensen | – | Pensiun |
| MF | Suleiman Abdullahi | Eintracht Braunschweig | Dipinjamkan |
| MF | Laurenz Dehl | Hallescher FC | Dipinjamkan |