| 2026-09-12 | M. Forss | Middlesbrough → Neftchi | Free agent |
| 2026-09-02 | A. Gilbert | Middlesbrough → Leyton Orient | Free agent |
| 2026-09-01 | M. Whittaker | Middlesbrough → Colorado Rapids | Transfer |
| 2026-08-31 | M. Whittaker | Middlesbrough → Colorado Rapids | Transfer |
| 2026-08-31 | A. Cozier-Duberry | Brighton → Middlesbrough | Loan |
| 2026-08-31 | F. Cartwright | Middlesbrough → Grimsby | Loan |
| 2026-08-31 | C. Barron | Rangers → Middlesbrough | Loan |
| 2026-08-30 | R. Pukštas | HNK Hajduk Split → Middlesbrough | Transfer |
| 2026-08-29 | A. Kanté | Middlesbrough → Al-Ettifaq | Transfer |
| 2026-08-29 | R. Pukštas | HNK Hajduk Split → Middlesbrough | Transfer |
| 2026-08-29 | J. Daley | Middlesbrough → Gillingham | Loan |
| 2026-08-28 | A. Kanté | Middlesbrough → Al-Ettifaq | Transfer |
| 2026-08-23 | S. Byram | Leeds → Middlesbrough | Free agent |
| 2026-08-22 | S. Byram | Leeds → Middlesbrough | Free agent |
| 2026-08-19 | S. Hansen | Middlesbrough → Gaziantep FK | Loan |
| 2026-08-16 | S. Dieng | Middlesbrough → Atromitos | Free agent |
| 2026-08-15 | S. Dieng | Middlesbrough → Atromitos | Free agent |
| 2026-08-14 | A. Phillips | Tottenham → Middlesbrough | Transfer |
| 2026-08-13 | A. Phillips | Tottenham → Middlesbrough | Transfer |
| 2026-08-09 | Finley Munroe | Middlesbrough → Blackpool | Loan |
| 2026-08-07 | K. Sène | Middlesbrough → BSC Young Boys | Transfer |
| 2026-08-07 | R. Vítek | Manchester United → Middlesbrough | Transfer |
| 2026-08-06 | D. Burgzorg | Middlesbrough → Preston | Loan |
| 2026-08-06 | K. Sène | Middlesbrough → BSC Young Boys | Transfer |
| 2026-08-06 | R. Vítek | Manchester United → Middlesbrough | Transfer |
| 2026-08-03 | M. Arfsten | Columbus Crew → Middlesbrough | Transfer |
| 2026-08-02 | M. Arfsten | Columbus Crew → Middlesbrough | Transfer |
| 2026-07-30 | S. Silvera | Middlesbrough → Milton Keynes Dons | Free agent |
| 2026-07-27 | S. Berhalter | Vancouver Whitecaps → Middlesbrough | Transfer |
| 2026-07-26 | S. Berhalter | Vancouver Whitecaps → Middlesbrough | Transfer |
| 2026-07-25 | S. Finch | Middlesbrough → South Shields | Transfer |
| 2026-07-25 | N. Fisher | Middlesbrough → Hartlepool | Free agent |
| 2026-07-24 | N. Fisher | Middlesbrough → Hartlepool | Free agent |
| 2026-07-23 | A. Baptiste | Middlesbrough → Harrogate Town | Transfer |
| 2026-07-22 | A. Baptiste | Middlesbrough → Harrogate Town | Transfer |
| 2026-07-21 | W. Lankshear | Tottenham → Middlesbrough | Transfer |
| 2026-07-09 | K. Joseph | Hull City → Middlesbrough | Transfer |
| 2026-07-03 | D. Barlaser | Middlesbrough → Milton Keynes Dons | Free agent |
| 2026-07-02 | D. Fry | Middlesbrough → Birmingham | Free agent |
| 2026-07-01 | D. Fry | Middlesbrough → Birmingham | Free agent |
| 2026-06-30 | J. Sarmiento | Brighton → Middlesbrough | Transfer |
| 2026-06-30 | H. Hackney | Middlesbrough → Everton | Transfer |
| 2026-06-30 | M. Peart-Harris | Oxford United → Middlesbrough | Free agent |
| 2026-06-29 | S. Silvera | Middlesbrough → Silvera Sam | Free agent |
| 2026-06-29 | S. Silvera | Middlesbrough → Milton Keynes Dons | Free agent |
| 2026-06-29 | M. Forss | Middlesbrough → Forss Marcus | Free agent |
| 2026-06-29 | A. Gilbert | Middlesbrough → Gilbert Alex | Free agent |
| 2026-06-29 | A. Gilbert | Middlesbrough → Leyton Orient | Free agent |
| 2026-06-29 | D. Burgzorg | Bristol City → Middlesbrough | Return from loan |
| 2026-06-29 | D. Barlaser | Middlesbrough → Milton Keynes Dons | Free agent |
| 2026-06-29 | D. Lenihan | Middlesbrough → Lenihan Darragh | Free agent |
| 2026-06-29 | M. Targett | Middlesbrough → Newcastle | Return from loan |
| 2026-06-29 | A. Kanté | Saint Etienne → Middlesbrough | Return from loan |
| 2026-06-29 | J. McLaughlin | Middlesbrough → McLaughlin Jon | Free agent |
| 2026-06-29 | J. Sarmiento | Middlesbrough → Brighton | Return from loan |
| 2026-06-29 | Will McPartland | Middlesbrough → Sheffield Wednesday | Free agent |
| 2026-05-30 | Neto Borges | Bristol City → Middlesbrough | Return from loan |
| 2026-05-30 | M. Forss | Bolton → Middlesbrough | Return from loan |
| 2026-05-30 | S. Finch | South Shields → Middlesbrough | Return from loan |
| 2026-05-30 | D. Barlaser | Hibernian → Middlesbrough | Return from loan |
| 2026-05-30 | A. Browne | Middlesbrough → Sunderland | Return from loan |
| 2026-05-30 | J. Carbon | Ross County → Middlesbrough | Return from loan |
| 2026-05-30 | J. Wildsmith | Middlesbrough → West Brom | Return from loan |
| 2026-05-30 | A. Baptiste | Rochdale → Middlesbrough | Return from loan |
| 2026-03-26 | A. Baptiste | Middlesbrough → Rochdale | Loan |
| 2026-03-05 | S. Dieng | Sheffield Wednesday → Middlesbrough | Return from loan |
| 2026-02-28 | S. Dieng | Sheffield Wednesday → Middlesbrough | Return from loan |
| 2026-02-19 | S. Dieng | Middlesbrough → Sheffield Wednesday | Loan |
| 2026-02-01 | S. Nypan | Middlesbrough → Manchester City | Return from loan |
| 2026-02-01 | J. Wildsmith | West Brom → Middlesbrough | Loan |
| 2026-01-31 | Lord Listowell Hinneh | Asante Kotoko → Middlesbrough | - |
| 2026-01-31 | J. Carbon | Middlesbrough → Ross County | Loan |
| 2026-01-29 | A. Kanté | Middlesbrough → Saint Etienne | Loan |
| 2026-01-28 | D. Burgzorg | Middlesbrough → Bristol City | Loan |
| 2026-01-27 | J. Sarmiento | Brighton → Middlesbrough | Loan |
| 2026-01-16 | C. Lennon | Middlesbrough → Barnsley | Transfer |
| 2026-01-15 | L. Engel | Middlesbrough → Real Salt Lake | Transfer |
| 2026-01-14 | Finley Munroe | Aston Villa → Middlesbrough | Transfer |
| 2026-01-12 | S. Finch | Middlesbrough → South Shields | Loan |
| 2026-01-08 | Leo Castledine | Chelsea → Middlesbrough | Transfer |
| 2026-01-04 | L. McCabe | Plymouth → Middlesbrough | Return from loan |
| 2026-01-02 | C. Lennon | Darlington 1883 → Middlesbrough | Return from loan |
31S. BrynnGoalkeeper · 25
33J. McLaughlinGoalkeeper · 38
1R. VítekGoalkeeper · 22
12L. AylingDefender · 34
2C. BrittainDefender · 27
3S. ByramDefender · 32
25G. EdmundsonDefender · 28
5A. JonesDefender · 28
29A. MalandaDefender · 24
30Neto BorgesDefender · 29
4A. PhillipsDefender · 20
18C. BarronMidfielder · 23
6S. BerhalterMidfielder · 24
19Leo CastledineMidfielder · 20
28L. McCabeMidfielder · 19
8R. McGreeMidfielder · 27
10A. MorrisMidfielder · 24
14M. Peart-HarrisMidfielder · 23
21R. PukštasMidfielder · 21
17M. ArfstenDefender · 24
9T. ConwayAttacker · 23
11A. Cozier-DuberryAttacker · 20
22K. JosephAttacker · 24
7W. LankshearAttacker · 20
16J. SarmientoAttacker · 23
13D. StrelecAttacker · 24