| Transactions |
| Date | Team | Player | Type | OthTm | EffDate | When |
| 2/19/2021 | AH | Margot | Acquired via trade | BTB | | After |
| 2/19/2021 | AH | Merrifield | Traded away | BTB | | After |
| 2/19/2021 | BTB | Margot | Traded away | AH | | After |
| 2/19/2021 | BTB | Merrifield | Acquired via trade | AH | | After |
| 2/24/2021 | BTB | Melancon | Traded away | VD | | After |
| 2/24/2021 | BTB | Scott | Acquired via trade | VD | | After |
| 2/24/2021 | VD | Melancon | Acquired via trade | BTB | | After |
| 2/24/2021 | VD | Scott | Traded away | BTB | | After |
| 2/26/2021 | BC | Colome | Traded away | BTB | | After |
| 2/26/2021 | BC | Suero | Acquired via trade | BTB | | After |
| 2/26/2021 | BTB | Colome | Acquired via trade | BC | | After |
| 2/26/2021 | BTB | Suero | Traded away | BC | | After |
| 3/13/2021 | ACS | Diaz,Ed | Acquired via trade | AH | | After |
| 3/13/2021 | ACS | Holland,G | Traded away | AH | | After |
| 3/13/2021 | AH | Diaz,Ed | Traded away | ACS | | After |
| 3/13/2021 | AH | Holland,G | Acquired via trade | ACS | | After |
| 3/19/2021 | BTB | Cole,G | Acquired via trade | HS | | After |
| 3/19/2021 | BTB | Glasnow | Traded away | HS | | After |
| 3/19/2021 | HS | Cole,G | Traded away | BTB | | After |
| 3/19/2021 | HS | Glasnow | Acquired via trade | BTB | | After |
| 3/25/2021 | ACS | Bemboom | Acquired via trade | VD | | After |
| 3/25/2021 | ACS | Schwarber | Traded away | VD | | After |
| 3/25/2021 | AH | Holland,G | Traded away | End | | After |
| 3/25/2021 | BC | Harper,B | Traded away | HS | | After |
| 3/25/2021 | BC | Marte,K | Acquired via trade | HS | | 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 |
| 4/9/2021 | BTB | Happ,JA | Demoted to reserve roster | | | Before |
| 4/9/2021 | BTB | Moustakas | Promoted to active roster | | | Before |
| 4/11/2021 | MSB | Arozarena | Demoted to reserve roster | | | Before |
| 4/11/2021 | MSB | Paredes,I | Demoted to reserve roster | | | Before |
| 4/15/2021 | BTB | Happ,JA | Promoted to active roster | | | Before |
| 4/15/2021 | BTB | Moustakas | Demoted to reserve roster | | | Before |
| 4/17/2021 | PL | Hernandez,El | Promoted to active roster | | | Before |
| 4/17/2021 | PL | Wisler | Demoted to reserve roster | | | Before |
| 4/18/2021 | BB | Wilson,B | Demoted to reserve roster | | | Before |
| 4/23/2021 | AH | Huff | Released | | | Before |
| 4/23/2021 | AH | Huff | Demoted to reserve roster | | | Before |
| 4/24/2021 | AH | Chisholm | Acquired via trade | BB | | After |
| 4/24/2021 | AH | Luzardo | Acquired via trade | BB | | After |
| 4/24/2021 | AH | Plesac | Traded away | BB | | After |
| 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 | AH | Luzardo | Promoted to active roster | | | Before |
| 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 |
| 5/2/2021 | BTB | Moustakas | Promoted to active roster | | | Before |
| 5/2/2021 | BTB | Senzatela | Demoted to reserve roster | | | Before |
| 5/5/2021 | BC | Chapman,A | Demoted to reserve roster | | | Before |
| 5/6/2021 | SFR | Alcantara,Sa | Promoted to active roster | | | Before |
| 5/6/2021 | SFR | Antone | Promoted to active roster | | | Before |
| 5/6/2021 | SFR | Perez,O | Demoted to reserve roster | | | Before |
| 5/6/2021 | SFR | Singer | Demoted to reserve roster | | | Before |
| 5/9/2021 | SFR | Antone | Demoted to reserve roster | | | Before |
| 5/9/2021 | SFR | Antone | Promoted to active roster | | | Before |
| 5/9/2021 | SFR | Bleier | Promoted to active roster | | | Before |
| 5/9/2021 | SFR | Sanchez,S | Demoted to reserve roster | | | Before |
| 5/12/2021 | PL | Gomber | Promoted to active roster | | | Before |
| 5/12/2021 | PL | Valdez,F | Demoted to reserve roster | | | Before |
| 5/12/2021 | PL | Wisler | Promoted to active roster | | | Before |
| 5/12/2021 | SFR | Antone | Demoted to reserve roster | | | Before |
| 5/12/2021 | SFR | Perez,O | Promoted to active roster | | | Before |
| 5/14/2021 | ACS | Bohm | Demoted to reserve roster | | | Before |
| 5/14/2021 | ACS | Diaz,Y | Promoted to active roster | | | Before |
| 5/15/2021 | BTB | Moustakas | Demoted to reserve roster | | | Before |
| 5/15/2021 | BTB | Senzatela | Promoted to active roster | | | Before |
| 5/18/2021 | ACS | Bohm | Traded away | WN | | After |
| 5/18/2021 | ACS | Hosmer | Acquired via trade | WN | | After |
| 5/18/2021 | ACS | Leiter | Traded away | WN | | After |
| 5/18/2021 | PL | Gausman | Demoted to reserve roster | | | Before |
| 5/18/2021 | WN | Bohm | Acquired via trade | ACS | | After |
| 5/18/2021 | WN | Hosmer | Traded away | ACS | | After |
| 5/18/2021 | WN | Leiter | Acquired via trade | ACS | | After |
| 5/19/2021 | ACS | Madrigal | Demoted to reserve roster | | | Before |
| 5/21/2021 | AH | Candelario | Traded away | BTB | | After |
| 5/21/2021 | AH | Longoria | Acquired via trade | BTB | | After |
| 5/21/2021 | BTB | Candelario | Acquired via trade | AH | | After |
| 5/21/2021 | BTB | Clevinger | Acquired via trade | VD | | After |
| 5/21/2021 | BTB | Happ,JA | Traded away | VD | | After |
| 5/21/2021 | BTB | Longoria | Traded away | AH | | After |
| 5/21/2021 | VD | Clevinger | Traded away | BTB | | After |
| 5/21/2021 | VD | Happ,JA | Acquired via trade | BTB | | After |
| 5/22/2021 | PL | Gausman | Promoted to active roster | | | Before |
| 5/22/2021 | PL | Wisler | Demoted to reserve roster | | | Before |
| 5/24/2021 | ACS | Madrigal | Traded away | BB | | After |
| 5/24/2021 | BB | Madrigal | Acquired via trade | ACS | | After |
| 5/28/2021 | SFR | Alcantara,Sa | Demoted to reserve roster | | | Before |
| 5/28/2021 | SFR | Singer | Promoted to active roster | | | Before |
| 6/1/2021 | BB | Almonte,Y | Traded away | End | | After |
| 6/1/2021 | BB | Iglesias,R | Acquired via trade | End | | After |
| 6/1/2021 | BTB | Bellinger | Traded away | End | | After |
| 6/1/2021 | BTB | Gallen | Acquired via trade | End | | After |
| 6/1/2021 | BTB | Senzatela | Traded away | End | | After |
| 6/1/2021 | BTB | Story | 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 | BTB | Cervelli | Acquired via trade | End | | After |
| 6/2/2021 | BTB | Grandal | Traded away | End | | After |
| 6/2/2021 | End | Cervelli | Traded away | BTB | | After |
| 6/2/2021 | End | Grandal | Acquired via trade | BTB | | After |
| 6/3/2021 | ACS | deGrom | Traded away | HS | | After |
| 6/3/2021 | ACS | Ryu | Acquired via trade | HS | | After |
| 6/3/2021 | ACS | Seager,C | Acquired via trade | HS | | 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 |
| 6/3/2021 | WN | Adell | Acquired via trade | HS | | After |
| 6/3/2021 | WN | Davis | Acquired via trade | HS | | After |
| 6/3/2021 | WN | Ryu | Traded away | HS | | After |
| 6/4/2021 | ACS | Gregorius | Demoted to reserve roster | | | Before |
| 6/8/2021 | HS | Graterol | Promoted to active roster | | | Before |
| 6/9/2021 | BTB | Bradley,J | Acquired via trade | ShS | | After |
| 6/9/2021 | BTB | Jeffress | Acquired via trade | ShS | | After |
| 6/9/2021 | BTB | Lynn | Traded away | ShS | | After |
| 6/9/2021 | BTB | Rodriguez,R | Traded away | ShS | | After |
| 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 |
| 6/22/2021 | ACS | Garcia,Ja | Demoted to reserve roster | | | Before |
| 6/22/2021 | ACS | Sims | Promoted to active roster | | | Before |
| 7/11/2021 | AH | Rucker | Traded away | ShS | | After |
| 7/11/2021 | ShS | Rucker | Acquired via trade | AH | | After |
| 7/15/2021 | VD | Schwarber | Promoted to active roster | | | Before |
| 7/23/2021 | ACS | Darvish | Traded away | PL | | After |
| 7/23/2021 | ACS | Gausman | Acquired via trade | PL | | After |
| 7/23/2021 | ACS | Gregorius | Traded away | PL | | After |
| 7/23/2021 | ACS | Valdez,F | Acquired via trade | PL | | After |
| 7/23/2021 | PL | Darvish | Acquired via trade | ACS | | After |
| 7/23/2021 | PL | Gausman | Traded away | ACS | | After |
| 7/23/2021 | PL | Gregorius | Acquired via trade | ACS | | After |
| 7/23/2021 | PL | Valdez,F | Traded away | ACS | | After |
| 7/24/2021 | PL | Crawford,B | Demoted to reserve roster | | | Before |
| 7/24/2021 | PL | Darvish | Demoted to reserve roster | | | Before |
| 7/24/2021 | PL | Gregorius | Promoted to active roster | | | Before |
| 7/24/2021 | PL | Wisler | Promoted to active roster | | | Before |
| 7/28/2021 | ACS | Mahle | Acquired via trade | BB | | After |
| 7/28/2021 | ACS | Nola,Aa | Traded away | BB | | After |
| 7/28/2021 | BB | Mahle | Traded away | ACS | | After |
| 7/28/2021 | BB | Nola,Aa | Acquired via trade | ACS | | After |
| 7/28/2021 | PL | Darvish | Promoted to active roster | | | Before |
| 7/28/2021 | PL | Wisler | Demoted to reserve roster | | | Before |
| 7/29/2021 | ACS | Valdez,F | Promoted to active roster | | | Before |
| 7/29/2021 | BB | Giolito | Demoted to reserve roster | | | Before |
| 8/4/2021 | ACS | Antone | Acquired via trade | SFR | | After |
| 8/4/2021 | ACS | Garcia,Ja | Traded away | SFR | | After |
| 8/4/2021 | ACS | Pomeranz | Traded away | SFR | | After |
| 8/4/2021 | ACS | Treinen | Acquired via trade | SFR | | After |
| 8/4/2021 | SFR | Antone | Traded away | ACS | | After |
| 8/4/2021 | SFR | Garcia,Ja | Acquired via trade | ACS | | After |
| 8/4/2021 | SFR | Pomeranz | Acquired via trade | ACS | | After |
| 8/4/2021 | SFR | Treinen | Traded away | ACS | | After |
| 8/5/2021 | ACS | Antone | Promoted to active roster | | | Before |
| 8/5/2021 | ACS | Sims | Demoted to reserve roster | | | Before |
| 8/5/2021 | ACS | Treinen | Promoted to active roster | | | Before |
| 8/6/2021 | SFR | Garcia,Ja | Demoted to reserve roster | | | Before |
| 8/6/2021 | SFR | Garcia,Ja | Promoted to active roster | | | Before |
| 8/6/2021 | SFR | Romano,J | Demoted to reserve roster | | | Before |
| 8/22/2021 | ACS | Sims | Promoted to active roster | | | Before |
| 8/22/2021 | ACS | Treinen | Demoted to reserve roster | | | Before |
| 9/4/2021 | SFR | Castillo,L | Promoted to active roster | | | Before |
| 9/4/2021 | SFR | Naylor | Demoted to reserve roster | | | Before |
| 9/4/2021 | SFR | Sanchez,S | Promoted to active roster | | | Before |
| 9/4/2021 | SFR | Singer | Demoted to reserve roster | | | Before |
| 9/9/2021 | SFR | Bard,D | Demoted to reserve roster | | | Before |
| 9/9/2021 | SFR | Garcia,Ja | Promoted to active roster | | | Before |
| 9/11/2021 | SFR | Bader | Demoted to reserve roster | | | Before |
| 9/11/2021 | SFR | Bard,D | Promoted to active roster | | | Before |
| 9/20/2021 | ACS | Mahle | Promoted to active roster | | | Before |
| 9/20/2021 | ACS | Valdez,F | 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 |