| 07 Aug 19 | S. Stubbs Sam Stubbs |  MiddlesbroughMID | → |  Hamilton AcademicalHAM | Loan |
| 07 Aug 19 | A. Dijksteel Anfernee Dijksteel |  Charlton AthleticCHA | → | MiddlesbroughMID | Undisclosed |
| 07 Aug 19 | S. Stubbs Sam Stubbs | MiddlesbroughMID | → | Hamilton AcademicalHAM | Loan |
| 26 Jul 19 | M. Browne Marcus Browne |  West Ham UnitedWHU | → | MiddlesbroughMID | Undisclosed |
| 26 Jul 19 | M. Browne Marcus Browne | West Ham UnitedWHU | → | MiddlesbroughMID | Undisclosed |
| 26 Jul 19 | L. Armstrong Luke Armstrong | MiddlesbroughMID | → |  Salford CitySAL | Undisclosed |
| 24 Jul 19 | M. Braithwaite Martin Braithwaite | MiddlesbroughMID | → |  LeganésLEG | Undisclosed |
| 24 Jul 19 | M. Braithwaite Martin Braithwaite | MiddlesbroughMID | → | LeganésLEG | Undisclosed |
| 19 Jul 19 | A. Flint Aden Flint | MiddlesbroughMID | → |  Cardiff CityCAR | Undisclosed |
| 04 Jul 19 | T. Mejías Tomás Mejías | ONXOmonia NicosiaOmonia Nicosia | → | MiddlesbroughMID | Free |
| 01 Jul 19 | J. Mikel John Obi Mikel | MiddlesbroughMID | → |  TrabzonsporTRAB | Free |
| 01 Jul 19 | S. Downing Stewart Downing | MiddlesbroughMID | → |  Blackburn RoversBLK | Free |
| 07 Feb 19 | A. Lonergan Andy Lonergan | MiddlesbroughMID | → |  RochdaleROCH | Loan |
| 24 Jan 19 | J. Mikel John Obi Mikel | XXX | → | MiddlesbroughMID | Free |
| 11 Jan 19 | L. Armstrong Luke Armstrong | MiddlesbroughMID | → |  Accrington StanleyACCR | Loan |
| 09 Jan 19 | C. Ripley Connor Ripley | MiddlesbroughMID | → |  Preston North EndPNE | Undisclosed |
| 04 Jan 19 | N. McGinley Nathan McGinley | MiddlesbroughMID | → |  Forest Green RoversFGR | Loan |
| 03 Jan 19 | M. Braithwaite Martin Braithwaite | MiddlesbroughMID | → | LeganésLEG | Loan |
| 03 Jan 19 | M. Braithwaite Martin Braithwaite | MiddlesbroughMID | → | LeganésLEG | Loan |
| 01 Jan 19 | R. van La Parra Rajiv van La Parra |  Huddersfield TownHUD | → | MiddlesbroughMID | Loan |
| 01 Jan 19 | R. van La Parra Rajiv van La Parra | Huddersfield TownHUD | → | MiddlesbroughMID | Loan |