Steve Clarke's side eased into the third round of the Capital One Cup with a professional performance made more eye-catching by the Burundi-born winger's stellar contribution.
The 20-year-old academy product, who fled his war-ravaged home country as a 10-year-old, was by far and away his side's stand-out performer as he took the game to the Welsh side from the first minute to effectively wrap up the win before the half-time whistle had even blown.
Summer signing Scott Sinclair was one of five full debutants for Albion while third-choice goalkeeper Luke Daniels stood in for Ben Foster after he suffered a stress fracture in his foot.
Also making their first Albion starts were defender Diego Lugano and striker Matej Vydra.
Berahino put his side ahead just six minutes in after Sinclair and Vydra combined well.
He doubled his tally 20 minutes later with a lovely drive from the right of the box which left Newport goalkeeper Lenny Pidgeley with no chance.
And he completed the hat-trick from the penalty spot to put the game out of the reach of the Football League newcomers before the half was over.
A tepid second half saw Albion spurn chances through Chris Brunt and Markus Rosenberg as Newport had to settle for a respectable defeat.
Justin Edinburgh's visiting side started brightly as skipper Andy Sandell had the first chance but it was Albion who took the lead with a slick opener. Vydra fed Sinclair and the former Swansea man carried it on before slotting it through for Berahino, who showed pace and then poise to slip it past Pidgeley.
Sinclair and Berahino had chances to add to the lead before Newport's Adam Chapman fired just wide with a decent effort.
Conor Washington and Harry Worley both had further chances for the Welsh outfit before Berahino got his second in the 26th minute. In space towards the right, the youngster picked his spot before driving the ball into the top-right corner with his weaker left foot.
It was 3-0 before the break as Berahino completed his hat-trick from a penalty after Craig Dawson was wrestled down by Worley at a corner and referee Andy D'Urso pointed to the spot.
Vydra was forced off with a knock just before the break, replaced by Rosenberg, while Albion midfielder Claudio Yacob was perhaps lucky to only be booked for a careless challenge.
West Brom captain Brunt could have done better after good work by Rosenberg but shot wide in a pedestrian second half.
Rosenberg then missed a decent opportunity himself as the encounter petered out in front of just under 9,000 supporters.