The 21-year-old has only just returned from a loan spell at Tranmere Rovers.
During his time at Prenton Park, Jervis made five appearances and scored one goal.
Jervis left Tranmere with them top of League One, whereas Pompey are currently struggling in 21st place.
His move to Fratton Park will be the seventh time Jervis has spent time away from Blues in the last two years, following stints at Hereford United (twice), Notts County, Swindon Town, Preston North End, Carlisle United and Tranmere.
Guy Whittingham is the current caretaker manager at Pompey, following Michael Appleton's departure to Blackpool.