The 30-year-old, who has also represented Leeds United and Charlton Athletic, was a free agent after his Saints contract expired at the end of last season.
He becomes manager Tony Mowbray's third signing of the summer following the arrivals of Dean Whitehead and Jozsef Varga.
The Championship club have not yet confirmed the length of Richardson's contract.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Ipswich TownIpswich | 43 | 26 | 11 | 6 | 85 | 53 | 32 | 89 |
| 2 | Leicester CityLeicester | 42 | 28 | 4 | 10 | 79 | 38 | 41 | 88 |
| 3 | Leeds UnitedLeeds | 43 | 26 | 9 | 8 | 76 | 34 | 42 | 87 |
| 4 | Southampton | 42 | 25 | 9 | 8 | 84 | 54 | 30 | 84 |
| 5 | West Bromwich AlbionWest Brom | 43 | 20 | 12 | 11 | 66 | 42 | 24 | 72 |
| 6 | Norwich CityNorwich | 43 | 21 | 8 | 14 | 76 | 60 | 16 | 71 |
| 7 | Hull City | 42 | 18 | 11 | 13 | 62 | 54 | 8 | 65 |
| 8 | Coventry CityCoventry | 42 | 17 | 12 | 13 | 66 | 52 | 14 | 63 |
| 9 | Middlesbrough | 43 | 18 | 9 | 16 | 61 | 56 | 5 | 63 |
| 10 | Preston North EndPreston | 43 | 18 | 9 | 16 | 56 | 60 | -4 | 63 |
| 11 | Cardiff CityCardiff | 43 | 18 | 5 | 20 | 48 | 60 | -12 | 59 |
| 12 | Bristol City | 43 | 16 | 10 | 17 | 50 | 46 | 4 | 58 |
| 13 | Sunderland | 43 | 16 | 8 | 19 | 52 | 50 | 2 | 56 |
| 14 | Swansea CitySwansea | 43 | 14 | 11 | 18 | 53 | 62 | -9 | 53 |
| 15 | Watford | 43 | 12 | 16 | 15 | 59 | 58 | 1 | 52 |
| 16 | Millwall | 43 | 13 | 11 | 19 | 42 | 55 | -13 | 50 |
| 17 | Blackburn RoversBlackburn | 43 | 13 | 10 | 20 | 57 | 71 | -14 | 49 |
| 18 | Plymouth ArgylePlymouth | 43 | 12 | 12 | 19 | 58 | 66 | -8 | 48 |
| 19 | Queens Park RangersQPR | 43 | 12 | 11 | 20 | 40 | 57 | -17 | 47 |
| 20 | Stoke CityStoke | 43 | 12 | 11 | 20 | 41 | 60 | -19 | 47 |
| 21 | Birmingham CityBirmingham | 43 | 12 | 9 | 22 | 48 | 64 | -16 | 45 |
| 22 | Huddersfield TownHuddersfield | 43 | 9 | 17 | 17 | 47 | 70 | -23 | 44 |
| 23 | Sheffield WednesdaySheff Weds | 43 | 12 | 8 | 23 | 36 | 67 | -31 | 44 |
| R | Rotherham UnitedRotherham | 43 | 4 | 11 | 28 | 32 | 85 | -53 | 23 |
| > Championship Full Table | |||||||||
