Beaten by Warrington in their first Super 8s fixture, Widnes led 18-0 at half-time with tries from Chris Bridge, Lloyd White and Charly Runciman.
Corey Thompson crossed twice after the break, before Ben Heaton got two scores in reply for the hosts.
Joe Mellor, who scored in his 150th career game, and Danny Craven wrapped up the win late on.
Halifax: Sharp; Heaton, Barber, Tyrer, Worrincy; Murrell, Johnston; Morris, Kaye, Fairbank, Grady, Cahalane, Grix.
Replacements: Moore, Woodburn-Hall, Sio, Douglas.
Widnes Vikings: Hanbury; Marsh, Bridge, Runciman, Thompson; Craven, Mellor; Buchanan, White, Dudson, Houston, Whitley, Cahill.;
Replacements: Manuokafoa, J Chapelhow, Olbison, Johnstone.
Referee: Gareth Hewer
Widnes Vikings got their first win of the Qualifiers, scoring seven tries in a routine victory at Halifax.