The England Under-21 international fired home from an indirect free-kick as the Baggies recorded just a third home league win of the season
The future of in-form striker Berahino has been the subject of much speculation and Albion's leading scorer capped another lively display by firing home a deflected free-kick from inside the penalty area 13 minutes from time after Allan McGregor had picked up Ahmed Elmohamady's back-pass.
Berahino, who has been linked with the likes of Tottenham and Liverpool, scored four times in a 7-0 rout of Gateshead in the FA Cup third round last weekend and he was the stand-out player once again at The Hawthorns on Saturday.
Pulis has now won both games since replacing Alan Irvine at the helm, but Albion were anything but convincing in what was only their third home victory of the season in the top flight.
Victory for the Midlands club moved them above Hull into 14th in the table and was only their second Premier League success in their last 11 games.
Hull offered very little going forward and the loss of Nikica Jelavic and Abel Hernandez to injury in the first half will no doubt hasten Steve Bruce's attempts to bring in at least one striker, with Jermain Defoe and Yaya Sanogo mooted as targets.
Pulis handed midfielder Claudio Yacob only his second Premier League start of the season, while record signing Brown Ideye was preferred to Victor Anichebe in attack.
Jelavic recovered from illness to take his place in a Hull side that showed eight changes from the team which lost in the FA Cup at Arsenal last weekend.
After an uneventful start to the game it was Berahino who had the first opportunity when he played a one-two with Stephane Sessegnon before firing wide of the far post after 18 minutes.
Both sides looked devoid of ideas going forward in a drab first half, but Berahino remained lively and forced a save out of McGregor with a strike from 20 yards out after taking a pass from Chris Brunt.
Hull suffered a double blow when they lost Jelavic and Hernandez to injury before half-time, with Robbie Brady and Tom Ince replacing the strike duo.
Brady wasted no time in making an impact as he unleashed a left-foot strike from a tight angle which Ben Foster tipped over the crossbar.
Ideye then had the best chance of the game 42 minutes in, when Berahino's perfectly weighted first time pass sent the Nigeria striker clear but he failed to hit the target with a tame finish.
The dangerous Berahino caused the Hull defence more problems early in the second half when he flashed the ball across the face of the goal but there was nobody on hand to apply the finish.
Pulis was typically animated on the touchline as the home side continued to look short of ideas and Albion's fans grew increasingly frustrated.
Anichebe replaced the ineffective Ideye with 17 minutes remaining and moments later there was a nervous moment for a poor defensive header gifted Elmohamady with a chance to open the scoring, but his shot was blocked.
The Egyptian was in the thick of the action again as his needless back-pass was picked up by McGregor and Berahino rifled home a free-kick from around 10 yards which nicked off Jake Livermore on its way in to give Albion three precious points and take his impressive tally for the season to 14 goals.