The 21-year-old becomes Preston's eighth signing of the summer, arriving with over a century of professional appearances behind him despite injury having interrupted his time in England.
"It's a very exciting time. Everything's happened pretty quickly but I'm really looking forward to my time here. The minute that I was told that Preston were interested, I was instantly excited for this opportunity," Wiley said.
"I've had some great conversations with the manager already and it's clear what he wants from me. I'm looking forward to my time here and growing as a player."
Wiley came through Atlanta United's academy after joining at 11, making his debut for the club's USL Championship affiliate in 2020 before being promoted to the first team two years later, where he established himself as a playmaking left-back and earned his first USMNT caps.
Chelsea signed him from Atlanta on a six-year deal, but regular football has proven hard to find since: he spent his first season out on loan at Strasbourg in Ligue 1, before two separate loan spells at Watford in the Championship yielded just 15 appearances combined, largely because of a shoulder injury and its lingering effects.
Now fully fit, Wiley will look to establish himself as a regular for the first time since leaving Major League Soccer, wearing the number 12 shirt for Preston this season.
His arrival gives manager Paul Heckingbottom a genuine left-back option after a summer rebuild that has already brought in seven other new faces, with Wiley's athleticism and attacking instincts from full-back seen as a natural fit for a Preston side looking to play with more purpose going forward this season.