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 | 19 | 13 | 4 | 2 | 43 | 22 | 21 | 43 |
| 2 | Birmingham CityBirmingham | 18 | 13 | 3 | 2 | 34 | 16 | 18 | 42 |
| 3 | Wrexham | 20 | 12 | 5 | 3 | 30 | 13 | 17 | 41 |
| 4 | Huddersfield TownHuddersfield | 19 | 11 | 3 | 5 | 30 | 18 | 12 | 36 |
| 5 | Stockport CountyStockport | 20 | 9 | 6 | 5 | 32 | 21 | 11 | 33 |
| 6 | Reading | 19 | 9 | 4 | 6 | 30 | 28 | 2 | 31 |
| 7 | Barnsley | 20 | 8 | 6 | 6 | 29 | 26 | 3 | 30 |
| 8 | Bolton WanderersBolton | 18 | 9 | 3 | 6 | 28 | 29 | -1 | 30 |
| 9 | Lincoln CityLincoln | 20 | 7 | 7 | 6 | 26 | 25 | 1 | 28 |
| 10 | Blackpool | 19 | 7 | 5 | 7 | 29 | 31 | -2 | 26 |
| 11 | Mansfield TownMansfield | 18 | 7 | 4 | 7 | 22 | 22 | 0 | 25 |
| 12 | Stevenage | 18 | 7 | 4 | 7 | 15 | 17 | -2 | 25 |
| 13 | Peterborough UnitedPeterborough | 19 | 7 | 3 | 9 | 37 | 35 | 2 | 24 |
| 14 | Charlton AthleticCharlton | 19 | 6 | 6 | 7 | 18 | 19 | -1 | 24 |
| 15 | Exeter CityExeter | 19 | 7 | 3 | 9 | 17 | 21 | -4 | 24 |
| 16 | Wigan AthleticWigan | 19 | 6 | 5 | 8 | 17 | 16 | 1 | 23 |
| 17 | Rotherham UnitedRotherham | 18 | 6 | 5 | 7 | 19 | 20 | -1 | 23 |
| 18 | Leyton Orient | 19 | 6 | 4 | 9 | 19 | 20 | -1 | 22 |
| 19 | Northampton TownNorthampton | 20 | 5 | 6 | 9 | 21 | 29 | -8 | 21 |
| 20 | Bristol Rovers | 19 | 6 | 3 | 10 | 17 | 28 | -11 | 21 |
| 21 | Crawley TownCrawley | 19 | 5 | 4 | 10 | 20 | 32 | -12 | 19 |
| 22 | Cambridge UnitedCambridge | 19 | 4 | 5 | 10 | 20 | 31 | -11 | 17 |
| 23 | Burton Albion | 19 | 2 | 6 | 11 | 16 | 30 | -14 | 12 |
| 24 | Shrewsbury TownShrewsbury | 19 | 3 | 2 | 14 | 19 | 39 | -20 | 11 |
| > League One Full Table | |||||||||
