The 27-year-old full-back has penned a four-year contract at Elland Road, becoming the Whites' 10th addition of a busy summer transfer window under Daniel Farke.
Standing at 6ft, Justin brings valuable experience and versatility, capable of operating on either flank of the defence.
A product of hometown side Luton Town, he earned a move to Leicester in 2019 following a standout spell with the Hatters.
During his time with the Foxes, Justin enjoyed considerable success, including lifting the FA Cup and helping the club secure back-to-back fifth-place finishes in the Premier League, which ensured European qualification.
He featured in double figures across continental competitions, further underlining his pedigree at the highest level.
Now on the verge of his 100th Premier League appearance, Justin has made 99 top-flight outings to date. His consistency at club level was rewarded in 2022 when he earned his senior England debut, highlighting his rise from the lower leagues to the international stage.
Leeds supporters will be eager to see how Justin's blend of athleticism and tactical intelligence strengthens Farke's defensive options, particularly with his ability to play on both the right and left sides.