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 | 14 | 10 | 2 | 2 | 32 | 16 | 16 | 32 |
| 2 | Birmingham CityBirmingham | 13 | 9 | 3 | 1 | 24 | 12 | 12 | 30 |
| 3 | Wrexham | 14 | 8 | 4 | 2 | 22 | 10 | 12 | 28 |
| 4 | Barnsley | 14 | 7 | 4 | 3 | 23 | 18 | 5 | 25 |
| 5 | Lincoln CityLincoln | 14 | 7 | 4 | 3 | 21 | 17 | 4 | 25 |
| 6 | Stockport CountyStockport | 15 | 6 | 6 | 3 | 25 | 17 | 8 | 24 |
| 7 | Mansfield TownMansfield | 13 | 7 | 3 | 3 | 20 | 15 | 5 | 24 |
| 8 | Huddersfield TownHuddersfield | 14 | 7 | 2 | 5 | 21 | 14 | 7 | 23 |
| 9 | Reading | 14 | 7 | 2 | 5 | 22 | 21 | 1 | 23 |
| 10 | Bolton WanderersBolton | 14 | 7 | 2 | 5 | 22 | 24 | -2 | 23 |
| 11 | Exeter CityExeter | 13 | 7 | 1 | 5 | 14 | 10 | 4 | 22 |
| 12 | Peterborough UnitedPeterborough | 15 | 6 | 3 | 6 | 31 | 27 | 4 | 21 |
| 13 | Charlton AthleticCharlton | 14 | 5 | 4 | 5 | 15 | 15 | 0 | 19 |
| 14 | Stevenage | 15 | 5 | 3 | 7 | 11 | 16 | -5 | 18 |
| 15 | Rotherham UnitedRotherham | 15 | 4 | 5 | 6 | 14 | 18 | -4 | 17 |
| 16 | Bristol Rovers | 14 | 5 | 2 | 7 | 16 | 21 | -5 | 17 |
| 17 | Northampton TownNorthampton | 14 | 4 | 4 | 6 | 18 | 21 | -3 | 16 |
| 18 | Blackpool | 14 | 4 | 4 | 6 | 21 | 28 | -7 | 16 |
| 19 | Wigan AthleticWigan | 14 | 3 | 5 | 6 | 12 | 12 | 0 | 14 |
| 20 | Leyton Orient | 14 | 4 | 2 | 8 | 14 | 18 | -4 | 14 |
| 21 | Crawley TownCrawley | 15 | 3 | 3 | 9 | 14 | 27 | -13 | 12 |
| 22 | Cambridge UnitedCambridge | 13 | 3 | 1 | 9 | 12 | 23 | -11 | 10 |
| 23 | Burton Albion | 14 | 1 | 5 | 8 | 15 | 25 | -10 | 8 |
| 24 | Shrewsbury TownShrewsbury | 15 | 2 | 2 | 11 | 13 | 27 | -14 | 8 |
| > League One Full Table | |||||||||
