The Northern Ireland international will officially be unveiled by the Hornets on July 1 when his contract with Blackpool expires.
It will be the second time that Cathcart has turned out for Watford, having spent time on loan at Vicarage Road while on the books of Manchester United in 2009.
The 25-year-old has agreed a two-year deal.
Restore Data
| Team | P | W | D | L | F | A | GD | PTS | |
| 1 | Leeds UnitedLeeds | 27 | 16 | 8 | 3 | 51 | 19 | 32 | 56 |
| 2 | Sheffield UnitedSheff Utd | 27 | 17 | 6 | 4 | 38 | 17 | 21 | 55 |
| 3 | Burnley | 27 | 14 | 11 | 2 | 31 | 9 | 22 | 53 |
| 4 | Sunderland | 27 | 14 | 9 | 4 | 39 | 22 | 17 | 51 |
| 5 | Blackburn RoversBlackburn | 27 | 12 | 6 | 9 | 31 | 24 | 7 | 42 |
| 6 | West Bromwich AlbionWest Brom | 27 | 9 | 14 | 4 | 33 | 22 | 11 | 41 |
| 7 | Middlesbrough | 27 | 11 | 8 | 8 | 44 | 34 | 10 | 41 |
| 8 | Watford | 27 | 12 | 5 | 10 | 38 | 37 | 1 | 41 |
| 9 | Bristol City | 27 | 9 | 10 | 8 | 33 | 31 | 2 | 37 |
| 10 | Sheffield WednesdaySheff Weds | 27 | 10 | 7 | 10 | 38 | 43 | -5 | 37 |
| 11 | Norwich CityNorwich | 27 | 9 | 9 | 9 | 43 | 39 | 4 | 36 |
| 12 | Queens Park RangersQPR | 27 | 8 | 11 | 8 | 30 | 34 | -4 | 35 |
| 13 | Swansea CitySwansea | 27 | 9 | 7 | 11 | 30 | 33 | -3 | 34 |
| 14 | Coventry CityCoventry | 27 | 8 | 8 | 11 | 35 | 37 | -2 | 32 |
| 15 | Oxford UnitedOxford Utd | 27 | 8 | 8 | 11 | 30 | 41 | -11 | 32 |
| 16 | Preston North EndPreston | 27 | 6 | 13 | 8 | 28 | 34 | -6 | 31 |
| 17 | Millwall | 26 | 7 | 9 | 10 | 24 | 24 | 0 | 30 |
| 18 | Stoke CityStoke | 27 | 6 | 10 | 11 | 25 | 33 | -8 | 28 |
| 19 | Derby CountyDerby | 27 | 7 | 6 | 14 | 31 | 37 | -6 | 27 |
| 20 | Cardiff CityCardiff | 27 | 6 | 9 | 12 | 29 | 41 | -12 | 27 |
| 21 | Hull City | 27 | 6 | 8 | 13 | 26 | 36 | -10 | 26 |
| 22 | Portsmouth | 26 | 6 | 8 | 12 | 32 | 45 | -13 | 26 |
| 23 | Luton TownLuton | 27 | 7 | 5 | 15 | 27 | 44 | -17 | 26 |
| 24 | Plymouth ArgylePlymouth | 27 | 4 | 9 | 14 | 25 | 55 | -30 | 21 |
| > Championship Full Table | |||||||||
