Berahino, who signed for the Cobblers in October, has gone back to The Hawthorns.
He was set to play his final game for Aidy Boothroyd's side against Macclesfield at Sixfields on Saturday but the fixture was postponed. The 18-year-old made 15 appearances in all competitions for Northampton, scoring six goals.
It was thought Boothroyd could attempt to bring Berahino back to the club now that the loan transfer window is open again.
However, the Cobblers boss said: "Saido has gone back to West Brom and he will be joining a club in League One.
"He has done very well for us but he is a young man and you can understand him wanting to play at a higher level. I would like to thank him for his contribution and I wish him well for the future but we draw a line under that now and move on."
