"I'm delighted to sign Yassin and we have very high hopes for him," said Addicks manager AlanPardew.
"He's a player that a number of clubs were very interested in and we're naturally very pleased he has chosen Charlton.
"He brings exactly the qualities we are going to need in the Championship next season. He's a very honest player who wants to succeed and he has plenty of hunger.
"He's a player I've been aware of some seven months now and he's going to be a great addition to our squad for next year."