After a goalless first half, Joe Lolley fired the visitors in front within a minute of the restart and they never looked back from that point.
Ward, who had been a first-half replacement for the injured Nakhi Wells, went on to score three times - twice as a result of errors from Hornets keeper Jonathan Bond - before Troy Deeney netted a late consolation from the penalty spot.
Watford gave a debut to Alex Jakubiak and the academy striker could have scored twice in the opening five minutes.
First, the teenager latched onto a Daniel Pudil through ball on the left side of the penalty area but dragged his shot across goal and wide. He was then put through on goal between two defenders by Ikechi Anya but his effort was kept out by the legs of Alex Smithies.
The visitors then came into the game but were restricted to long-range efforts, the best of which saw Adam Clayton hit a low drive from the edge of the penalty area which would have troubled Hornets keeper Bond had it not been blocked.
But, as the half wore on, it had an increasingly end-of-season feel to it. Both sides were unable to keep possession for long enough to build meaningful attacks and the quality of the fare degenerated as a result.
Having offered very little in the attacking third in the opening stages, the Hornets did have a good chance to take the lead in the 37th minute when a fine pass from newly-crowned player of the season Deeney released Cristian Battocchio but Paul Dixon did just enough to hold him up and in the end the midfielder's effort from a tight angle was blocked by the legs of Smithies.
Watford also reached an unwanted milestone before half-time when Tommie Hoban became the recipient of their 100th yellow card of the season for a foul on Adam Hammill.
Within 22 seconds off the restart though, Huddersfield were in front as Lolley wriggled away from Gabriele Angella before firing a shot across Bond and into the far corner to cap his full debut with a goal.
The Hornets keeper could not be faulted for that goal but he was to blame for what happened in the 55th minute, letting a routine shot from Ward from the right side of the penalty area squirm horribly through his legs to allow the Terriers to double their advantage.
Watford looked devoid of any fight at this stage and their afternoon was to get even worse in the 65th minute as Ward capitalised on some poor defending to score his second with a low right-footed shot.
That looked like it would be that but in the 87th minute Ward completed his hat-trick, whipping in a free-kick from the right with his left foot that again found Bond wanting as it beat him at his near post.
Watford did score a late consolation when they were awarded a soft penalty in the closing stages and Deeney fired home his 25th of the season from 12 yards.