| Transactions | ||||||
| Date | Team | Player | Type | OthTm | EffDate | When |
| 2/24/2021 | VD | Melancon | Acquired via trade | BTB | After | |
| 2/24/2021 | VD | Scott | Traded away | BTB | After | |
| 3/19/2021 | HS | Cole,G | Traded away | BTB | After | |
| 3/19/2021 | HS | Glasnow | Acquired via trade | BTB | After | |
| 3/25/2021 | End | Holland,G | Acquired via trade | AH | After | |
| 3/25/2021 | HS | Harper,B | Acquired via trade | BC | After | |
| 3/25/2021 | HS | Marte,K | Traded away | BC | After | |
| 3/25/2021 | VD | Bemboom | Traded away | ACS | After | |
| 3/25/2021 | VD | Schwarber | Acquired via trade | ACS | After | |
| 4/11/2021 | MSB | Arozarena | Demoted to reserve roster | Before | ||
| 4/11/2021 | MSB | Paredes,I | Demoted to reserve roster | Before | ||
| 4/18/2021 | BB | Wilson,B | Demoted to reserve roster | Before | ||
| 4/24/2021 | BB | Chisholm | Traded away | AH | After | |
| 4/24/2021 | BB | Luzardo | Traded away | AH | After | |
| 4/24/2021 | BB | Plesac | Acquired via trade | AH | After | |
| 4/25/2021 | BB | Mahle | Demoted to reserve roster | Before | ||
| 4/28/2021 | HS | Adell | Promoted to active roster | Before | ||
| 4/28/2021 | HS | Graterol | Demoted to reserve roster | Before | ||
| 5/21/2021 | VD | Clevinger | Traded away | BTB | After | |
| 5/21/2021 | VD | Happ,JA | Acquired via trade | BTB | After | |
| 5/24/2021 | BB | Madrigal | Acquired via trade | ACS | After | |
| 6/1/2021 | BB | Almonte,Y | Traded away | End | After | |
| 6/1/2021 | BB | Iglesias,R | Acquired via trade | End | After | |
| 6/1/2021 | End | Almonte,Y | Acquired via trade | BB | After | |
| 6/1/2021 | End | Bellinger | Acquired via trade | BTB | After | |
| 6/1/2021 | End | Gallen | Traded away | BTB | After | |
| 6/1/2021 | End | Iglesias,R | Traded away | BB | After | |
| 6/1/2021 | End | Senzatela | Acquired via trade | BTB | After | |
| 6/1/2021 | End | Story | Traded away | BTB | After | |
| 6/2/2021 | End | Cervelli | Traded away | BTB | After | |
| 6/2/2021 | End | Grandal | Acquired via trade | BTB | After | |
| 6/3/2021 | HS | Adell | Traded away | WN | After | |
| 6/3/2021 | HS | Davis | Traded away | WN | After | |
| 6/3/2021 | HS | deGrom | Acquired via trade | ACS | After | |
| 6/3/2021 | HS | Ryu | Traded away | ACS | After | |
| 6/3/2021 | HS | Ryu | Acquired via trade | WN | After | |
| 6/3/2021 | HS | Seager,C | Traded away | ACS | After | |
| 6/8/2021 | HS | Graterol | Promoted to active roster | Before | ||
| 6/9/2021 | ShS | Bradley,J | Traded away | BTB | After | |
| 6/9/2021 | ShS | Jeffress | Traded away | BTB | After | |
| 6/9/2021 | ShS | Lynn | Acquired via trade | BTB | After | |
| 6/9/2021 | ShS | Rodriguez,R | Acquired via trade | BTB | After | |
| 7/11/2021 | ShS | Rucker | Acquired via trade | AH | After | |
| 7/15/2021 | VD | Schwarber | Promoted to active roster | Before | ||
| 7/28/2021 | BB | Mahle | Traded away | ACS | After | |
| 7/28/2021 | BB | Nola,Aa | Acquired via trade | ACS | After | |
| 7/29/2021 | BB | Giolito | Demoted to reserve roster | Before | ||
| 9/27/2021 | BB | Madrigal | Promoted to active roster | Before | ||
| 9/27/2021 | BB | Sheffield | Demoted to reserve roster | Before | ||