The 21-year-old's previous deal with the Bluebirds was due to expire at the end of the season.
The youngster joined the Welsh outfit from Wycombe Wanderers in January 2012.
Harris, who spent part of the last campaign on loan at Brentford, has made two appearances for Cardiff this term.
Russell Slade's side continue their Championship campaign on Saturday when they entertain Rotherham United.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Leicester CityLeicester | 44 | 30 | 4 | 10 | 86 | 39 | 47 | 94 |
| 2 | Leeds UnitedLeeds | 44 | 27 | 9 | 8 | 80 | 37 | 43 | 90 |
| 3 | Ipswich TownIpswich | 43 | 26 | 11 | 6 | 85 | 53 | 32 | 89 |
| 4 | Southampton | 44 | 25 | 9 | 10 | 85 | 61 | 24 | 84 |
| 5 | West Bromwich AlbionWest Brom | 44 | 20 | 12 | 12 | 67 | 44 | 23 | 72 |
| 6 | Norwich CityNorwich | 44 | 21 | 9 | 14 | 77 | 61 | 16 | 72 |
| 7 | Hull City | 44 | 19 | 12 | 13 | 65 | 56 | 9 | 69 |
| 8 | Coventry CityCoventry | 43 | 17 | 12 | 14 | 68 | 55 | 13 | 63 |
| 9 | Middlesbrough | 44 | 18 | 9 | 17 | 64 | 60 | 4 | 63 |
| 10 | Preston North EndPreston | 44 | 18 | 9 | 17 | 56 | 61 | -5 | 63 |
| 11 | Cardiff CityCardiff | 44 | 19 | 5 | 20 | 50 | 61 | -11 | 62 |
| 12 | Bristol City | 44 | 16 | 11 | 17 | 51 | 47 | 4 | 59 |
| 13 | Sunderland | 44 | 16 | 8 | 20 | 52 | 51 | 1 | 56 |
| 14 | Swansea CitySwansea | 44 | 15 | 11 | 18 | 57 | 62 | -5 | 56 |
| 15 | Watford | 44 | 12 | 17 | 15 | 59 | 58 | 1 | 53 |
| 16 | Millwall | 44 | 14 | 11 | 19 | 43 | 55 | -12 | 53 |
| 17 | Stoke CityStoke | 44 | 13 | 11 | 20 | 44 | 60 | -16 | 50 |
| 18 | Queens Park RangersQPR | 44 | 13 | 11 | 20 | 41 | 57 | -16 | 50 |
| 19 | Blackburn RoversBlackburn | 44 | 13 | 10 | 21 | 58 | 74 | -16 | 49 |
| 20 | Plymouth ArgylePlymouth | 44 | 12 | 12 | 20 | 58 | 69 | -11 | 48 |
| 21 | Sheffield WednesdaySheff Weds | 44 | 13 | 8 | 23 | 39 | 68 | -29 | 47 |
| 22 | Birmingham CityBirmingham | 44 | 12 | 10 | 22 | 48 | 64 | -16 | 46 |
| 23 | Huddersfield TownHuddersfield | 44 | 9 | 17 | 18 | 47 | 74 | -27 | 44 |
| R | Rotherham UnitedRotherham | 44 | 4 | 12 | 28 | 32 | 85 | -53 | 24 |
| > Championship Full Table | |||||||||
