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 | |
| C | Leicester CityLeicester | 46 | 31 | 4 | 11 | 89 | 41 | 48 | 97 |
| P | Ipswich TownIpswich | 46 | 28 | 12 | 6 | 92 | 57 | 35 | 96 |
| 3 | Leeds UnitedLeeds | 46 | 27 | 9 | 10 | 81 | 43 | 38 | 90 |
| P | Southampton | 46 | 26 | 9 | 11 | 87 | 63 | 24 | 87 |
| 5 | West Bromwich AlbionWest Brom | 46 | 21 | 12 | 13 | 70 | 47 | 23 | 75 |
| 6 | Norwich CityNorwich | 46 | 21 | 10 | 15 | 79 | 64 | 15 | 73 |
| 7 | Hull City | 46 | 19 | 13 | 14 | 68 | 60 | 8 | 70 |
| 8 | Middlesbrough | 46 | 20 | 9 | 17 | 71 | 62 | 9 | 69 |
| 9 | Coventry CityCoventry | 46 | 17 | 13 | 16 | 70 | 59 | 11 | 64 |
| 10 | Preston North EndPreston | 46 | 18 | 9 | 19 | 56 | 67 | -11 | 63 |
| 11 | Bristol City | 46 | 17 | 11 | 18 | 53 | 51 | 2 | 62 |
| 12 | Cardiff CityCardiff | 46 | 19 | 5 | 22 | 53 | 70 | -17 | 62 |
| 13 | Millwall | 46 | 16 | 11 | 19 | 45 | 55 | -10 | 59 |
| 14 | Swansea CitySwansea | 46 | 15 | 12 | 19 | 59 | 65 | -6 | 57 |
| 15 | Watford | 46 | 13 | 17 | 16 | 61 | 61 | 0 | 56 |
| 16 | Sunderland | 46 | 16 | 8 | 22 | 52 | 54 | -2 | 56 |
| 17 | Stoke CityStoke | 46 | 15 | 11 | 20 | 49 | 60 | -11 | 56 |
| 18 | Queens Park RangersQPR | 46 | 15 | 11 | 20 | 47 | 58 | -11 | 56 |
| 19 | Blackburn RoversBlackburn | 46 | 14 | 11 | 21 | 60 | 74 | -14 | 53 |
| 20 | Sheffield WednesdaySheff Weds | 46 | 15 | 8 | 23 | 44 | 68 | -24 | 53 |
| 21 | Plymouth ArgylePlymouth | 46 | 13 | 12 | 21 | 59 | 70 | -11 | 51 |
| R | Birmingham CityBirmingham | 46 | 13 | 11 | 22 | 50 | 65 | -15 | 50 |
| R | Huddersfield TownHuddersfield | 46 | 9 | 18 | 19 | 48 | 77 | -29 | 45 |
| R | Rotherham UnitedRotherham | 46 | 5 | 12 | 29 | 37 | 89 | -52 | 27 |
| > Championship Full Table | |||||||||
