The 22-year-old, who has represented Scotland at Under-21 level, has agreed an 18-month contract at McDiarmid Park.
O'Halloran failed to make a league appearance during his time at the Reebok Stadium, with his two matches for the club coming in cup competitions.
The Glasgow-born forward has also enjoyed loan spells at Sheffield United and Tranmere Rovers.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Wycombe WanderersWycombe | 18 | 12 | 4 | 2 | 39 | 21 | 18 | 40 |
| 2 | Wrexham | 19 | 12 | 4 | 3 | 28 | 11 | 17 | 40 |
| 3 | Birmingham CityBirmingham | 17 | 12 | 3 | 2 | 32 | 16 | 16 | 39 |
| 4 | Huddersfield TownHuddersfield | 18 | 11 | 2 | 5 | 28 | 16 | 12 | 35 |
| 5 | Stockport CountyStockport | 19 | 9 | 6 | 4 | 31 | 19 | 12 | 33 |
| 6 | Reading | 18 | 9 | 4 | 5 | 30 | 25 | 5 | 31 |
| 7 | Bolton WanderersBolton | 17 | 9 | 3 | 5 | 28 | 27 | 1 | 30 |
| 8 | Barnsley | 19 | 7 | 6 | 6 | 27 | 25 | 2 | 27 |
| 9 | Lincoln CityLincoln | 19 | 7 | 6 | 6 | 24 | 23 | 1 | 27 |
| 10 | Mansfield TownMansfield | 17 | 7 | 3 | 7 | 22 | 22 | 0 | 24 |
| 11 | Exeter CityExeter | 18 | 7 | 3 | 8 | 16 | 19 | -3 | 24 |
| 12 | Charlton AthleticCharlton | 18 | 6 | 5 | 7 | 18 | 19 | -1 | 23 |
| 13 | Blackpool | 18 | 6 | 5 | 7 | 26 | 31 | -5 | 23 |
| 14 | Stevenage | 17 | 6 | 4 | 7 | 13 | 16 | -3 | 22 |
| 15 | Peterborough UnitedPeterborough | 18 | 6 | 3 | 9 | 33 | 32 | 1 | 21 |
| 16 | Leyton Orient | 18 | 6 | 3 | 9 | 19 | 20 | -1 | 21 |
| 17 | Northampton TownNorthampton | 19 | 5 | 6 | 8 | 21 | 26 | -5 | 21 |
| 18 | Bristol Rovers | 18 | 6 | 3 | 9 | 17 | 26 | -9 | 21 |
| 19 | Wigan AthleticWigan | 18 | 5 | 5 | 8 | 15 | 16 | -1 | 20 |
| 20 | Rotherham UnitedRotherham | 17 | 5 | 5 | 7 | 16 | 20 | -4 | 20 |
| 21 | Crawley TownCrawley | 18 | 5 | 4 | 9 | 17 | 28 | -11 | 19 |
| 22 | Cambridge UnitedCambridge | 18 | 4 | 4 | 10 | 18 | 29 | -11 | 16 |
| 23 | Burton Albion | 18 | 2 | 5 | 11 | 16 | 30 | -14 | 11 |
| 24 | Shrewsbury TownShrewsbury | 18 | 3 | 2 | 13 | 18 | 35 | -17 | 11 |
| > League One Full Table | |||||||||
