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 | Birmingham CityBirmingham | 23 | 16 | 5 | 2 | 41 | 17 | 24 | 53 |
| 2 | Wycombe WanderersWycombe | 25 | 15 | 6 | 4 | 50 | 27 | 23 | 51 |
| 3 | Wrexham | 25 | 15 | 6 | 4 | 37 | 18 | 19 | 51 |
| 4 | Huddersfield TownHuddersfield | 24 | 14 | 5 | 5 | 37 | 19 | 18 | 47 |
| 5 | Barnsley | 25 | 12 | 6 | 7 | 39 | 33 | 6 | 42 |
| 6 | Reading | 24 | 12 | 5 | 7 | 39 | 33 | 6 | 41 |
| 7 | Stockport CountyStockport | 25 | 10 | 8 | 7 | 37 | 27 | 10 | 38 |
| 8 | Leyton Orient | 24 | 11 | 4 | 9 | 32 | 22 | 10 | 37 |
| 9 | Mansfield TownMansfield | 23 | 11 | 4 | 8 | 31 | 26 | 5 | 37 |
| 10 | Bolton WanderersBolton | 24 | 11 | 4 | 9 | 36 | 37 | -1 | 37 |
| 11 | Charlton AthleticCharlton | 23 | 9 | 7 | 7 | 27 | 21 | 6 | 34 |
| 12 | Lincoln CityLincoln | 25 | 8 | 8 | 9 | 28 | 30 | -2 | 32 |
| 13 | Rotherham UnitedRotherham | 24 | 8 | 7 | 9 | 24 | 24 | 0 | 31 |
| 14 | Stevenage | 23 | 8 | 7 | 8 | 18 | 20 | -2 | 31 |
| 15 | Exeter CityExeter | 24 | 9 | 4 | 11 | 28 | 31 | -3 | 31 |
| 16 | Blackpool | 24 | 7 | 9 | 8 | 32 | 35 | -3 | 30 |
| 17 | Wigan AthleticWigan | 23 | 7 | 6 | 10 | 21 | 23 | -2 | 27 |
| 18 | Northampton TownNorthampton | 25 | 6 | 8 | 11 | 24 | 39 | -15 | 26 |
| 19 | Peterborough UnitedPeterborough | 24 | 7 | 4 | 13 | 41 | 46 | -5 | 25 |
| 20 | Bristol Rovers | 24 | 7 | 4 | 13 | 22 | 38 | -16 | 25 |
| 21 | Crawley TownCrawley | 23 | 5 | 5 | 13 | 24 | 43 | -19 | 20 |
| 22 | Shrewsbury TownShrewsbury | 24 | 4 | 5 | 15 | 24 | 44 | -20 | 17 |
| 23 | Cambridge UnitedCambridge | 24 | 4 | 5 | 15 | 22 | 43 | -21 | 17 |
| 24 | Burton Albion | 24 | 2 | 8 | 14 | 20 | 38 | -18 | 14 |
| > League One Full Table | |||||||||
