The 25-year-old midfielder has committed his future to Saints until the summer of 2025.
Ward-Prowse said: “I think everybody knows it’s a club that’s very close to my heart.
“I started out here as an eight-year-old and just had that goal of wanting to reach the first team, and my appreciation for the club is so big, because the people within it and the infrastructure has allowed me to follow my dream as a young boy who wanted to play professional football.
“They’ve given me every opportunity and every helping hand along the way to reach that target and for me again it’s another opportunity to repay that faith to everybody who’s played a part in my journey up until now.”
One-club man Ward-Prowse made his Southampton debut in October 2011 and has gone on to make 278 appearances, scoring 24 goals.
He has earned two caps for England, against Germany in 2017 and Montenegro last year.
Saints manager Ralph Hasenhuttl said: “Prowsey is a player who shows everything that Southampton Football Club is about.
“He has a passion for the club that everybody knows about, and he is respected by everyone here.
“I know he is a role model for our younger players especially, and these are all reasons why he was the right choice to be a long-term captain of this team and this club.”
