The 18 year old arrives after his departure from Championship Sheffield Wednesday, and will link up with the under-21s on a two-year deal.
Kakay rose through the ranks at Wednesday since he joined their youth set-up in the under-16s, and enjoyed an impressive 2024/25 campaign.
The youngster was a regular at under-18s level, featured for the under-21s, and gained experience in first team training with Danny Rohl’s side.
After signing for Saints, Kakay said: “It’s what I have worked hard for all my life to sign my first professional contract, I can’t wait to get started.
Sutura Kakay signing for Saints at Staplewood (Image: Stuart Martin / Southampton Football Club)
“With the history of the club bringing a lot of young players through, I thought this was the perfect pathway for me to exceed in my career.”
Director of group talent strategy, Andy Goldie added: “Sutura is another positive addition to the under-21s, adding quality and competition to our midfield pathway.
“He brings a different dynamic to the profile we already have, providing real athleticism and vision which he maximises particularly in transition.
“It was these qualities that are what attracted Mariela Nisotaki and her team to make him our first under-21s acquisition of the summer, and we look forward to developing those further over the next two seasons.”