Aljofree moves to Meadow Lane on-loan for the season.
Director of Football Roberto Gagliardi said: “Sonny has all the traits of a modern-day defender – balancing an aggressive playing style with the ability to distribute the ball from the back.
“He’s capable of playing anywhere across the defensive line, mainly being deployed in a back four for Manchester United but often on the right of a back three during his impressive loan at Accrington.
“Sonny’s maturity is reflected in the leadership roles he’s been given and the high esteem he’s held in by United. Combined with the fact he’s the son of former Plymouth defender, Hasney Aljofree, he has a very strong footballing pedigree.
“We faced strong competition from a number of League One clubs to sign him and we look forward to supporting his continued development.”