The promising 18-year-old centre-back has agreed a two-year contract and will join up with the club's senior pros after the summer.
Boro's Academy manager Dave Parnaby said: "We tracked Chris through his international programme with England, and a member of our recruitment staff forwarded very favourable reports from his performances with both England and Maidstone.
"I am very happy to announce that Chris has agreed a two-year contract with Middlesbrough.
"He is a very intelligent and level-headed young man who we feel has a lot of potential to fulfil.
"We look forward to him joining us in July for pre-season training."