The 30-year-old was a part of the Brentford side that secured promotion to the Championship last term.
However, he has opted to move to their league rivals on a two-year contract, which will come into force at the beginning of next month.
Donaldson, who has played for Hull City, York City, Hibernian and Crewe Alexandra, has become Lee Clark's ninth new addition of the summer.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Wycombe WanderersWycombe | 16 | 12 | 2 | 2 | 36 | 18 | 18 | 38 |
| 2 | Wrexham | 17 | 10 | 4 | 3 | 26 | 11 | 15 | 34 |
| 3 | Birmingham CityBirmingham | 15 | 10 | 3 | 2 | 28 | 15 | 13 | 33 |
| 4 | Stockport CountyStockport | 17 | 8 | 6 | 3 | 29 | 17 | 12 | 30 |
| 5 | Huddersfield TownHuddersfield | 16 | 9 | 2 | 5 | 25 | 15 | 10 | 29 |
| 6 | Barnsley | 17 | 7 | 6 | 4 | 26 | 22 | 4 | 27 |
| 7 | Reading | 16 | 8 | 3 | 5 | 26 | 24 | 2 | 27 |
| 8 | Bolton WanderersBolton | 16 | 8 | 3 | 5 | 25 | 26 | -1 | 27 |
| 9 | Lincoln CityLincoln | 17 | 7 | 5 | 5 | 23 | 21 | 2 | 26 |
| 10 | Mansfield TownMansfield | 15 | 7 | 3 | 5 | 20 | 17 | 3 | 24 |
| 11 | Exeter CityExeter | 16 | 7 | 2 | 7 | 14 | 15 | -1 | 23 |
| 12 | Charlton AthleticCharlton | 16 | 6 | 4 | 6 | 17 | 17 | 0 | 22 |
| 13 | Peterborough UnitedPeterborough | 16 | 6 | 3 | 7 | 32 | 29 | 3 | 21 |
| 14 | Bristol Rovers | 17 | 6 | 3 | 8 | 17 | 23 | -6 | 21 |
| 15 | Wigan AthleticWigan | 16 | 5 | 5 | 6 | 15 | 13 | 2 | 20 |
| 16 | Blackpool | 17 | 5 | 5 | 7 | 24 | 30 | -6 | 20 |
| 17 | Stevenage | 16 | 5 | 4 | 7 | 11 | 16 | -5 | 19 |
| 18 | Northampton TownNorthampton | 17 | 4 | 6 | 7 | 19 | 23 | -4 | 18 |
| 19 | Rotherham UnitedRotherham | 16 | 4 | 5 | 7 | 14 | 19 | -5 | 17 |
| 20 | Crawley TownCrawley | 17 | 4 | 4 | 9 | 15 | 27 | -12 | 16 |
| 21 | Leyton Orient | 16 | 4 | 3 | 9 | 14 | 20 | -6 | 15 |
| 22 | Cambridge UnitedCambridge | 16 | 3 | 4 | 9 | 14 | 25 | -11 | 13 |
| 23 | Shrewsbury TownShrewsbury | 16 | 3 | 2 | 11 | 16 | 29 | -13 | 11 |
| 24 | Burton Albion | 16 | 1 | 5 | 10 | 15 | 29 | -14 | 8 |
| > League One Full Table | |||||||||
