The France youth international, who joined the club from Stade Rennais FC’s academy in at the start of the 2015/16 campaign, has agreed a contract until the summer of 2018.
Valery, who has represented France at Under-17 level, has made 11 appearances for Craig Fleming’s Under-18s so far this season.
His form has earned him recognition at Under-21 level, making a substitute appearance against Norwich City at Carrow Road in November.
The Frenchman, who turned 17 last week, told youtube.com/southamptonfc
about his delight at agreeing to stay with the club for the next two seasons at least.
“I’m very happy signing my first professional contract with Southampton Football Club,” said the Frenchman.
“It’s a very good club for me to improve my football. All the staff are very good with me. I’m very happy.
“I have improved a lot already. These are great facilities for me to improve my football.
“I think it’s very important for a club to give chances to young players. When you are young it’s very important. That’s great for me to know.”