Scott Fitzgerald's fourth goal of the season gave Watford a deserved victory against their fellow Division One strugglers.
The Hornets dominated but had to wait until the 61st minute for the
breakthrough when Fitzgerald converted Micah Hyde's cross.
The result was enough to lift Watford out of the relegation zone, while Bradford have now taken just two points from their last seven matches.
Watford boss Ray Lewington handed a full home debut to Chelsea loan signing Lenny Pidgeley in place of suspended goalkeeper Alec Chamberlain but he was rarely tested until the closing stages.
Midfielder Paolo Vernazza returned after suspension and had the first chance but his shot from the edge of the area was blocked by David Wetherall.
Hyde was next to threaten but volleyed wide while a fierce drive from Devlin flew narrowly wide as Watford began to dominate.
The visitors failed to create a decent opening until the 23rd minute when Danny Forrest shot over the crossbar, while at the other end Bradford keeper Mark Paston kept out Marcus Gayle's header from a Neal Ardley corner.
Bradford defender Gareth Edds was booked for a foul on Danny Webber in the 39th minute, with Devlin firing wide from the resulting free-kick, while Webber forced a save from Paston just before the break.
Watford continued to dominate, although Webber and Hyde both fired over.
The Hornets grabbed the goal their pressure deserved just after the hour mark.
Devlin and Stephen Kelly linked well down the right wing, with the latter then sliding the ball through to Hyde and his cross was knocked in by Fitzgerald.
Bradford pressed forward in search of an equaliser and they almost drew level when Kearney's brilliant 30-yard volley was kept out by a tremendous save by Pidgeley.
The keeper also held a well-struck shot by substitute Rob Wolleaston before a free-kick by Paul Evans curled just wide of the far post and Watford held on for a much-needed win.
Watford: Pidgeley, Kelly, Cox, Gayle, Smith, Devlin, Hyde,
Ardley, Vernazza, Fitzgerald, Webber. Subs: Dyche, Dyer, Cook,
Bradford: Paston, Edds, Wetherall, Gavin, Jacobs, Summerbee,
Francis, Evans, Muirhead, Gray, Forrest. Subs: Combe, Kearney,
Wolleaston, McHugh, Standing.
Referee: U Rennie (S Yorkshire)