The 23-year-old arrives at the Kassam Stadium on a three-year deal for an undisclosed fee.
Tariqe Fosu Joins Oxford United
Fourth Summer Signing
Unlike Berkoe and Allardyce, who will likely feature in the U23 side, Fosu should slot straight into the first team.
Fosu had been offered a new deal by the Addicks. However, the winger rejected the opportunity to play for the newly promoted Championship side.
Instead, the 23-year-old opted to reunite his relationship with former manager Robinson, the man who brought him to the Valley two seasons ago.
Oxford fought off interest from Rotherham United and Lincoln City respectively to sign the winger, according to Richard Cawley of the South London Press.
Life Before Oxford
Fosu began his career at Reading, but in a three-year spell, he only made one appearance.
During his time with the Addicks, the winger, who can also play in an attacking midfield role, scored 11 goals in 57 appearances.
The winger’s best spell in South London came under Robinson, where he scored nine goals in his first season.