Stephenson, 20, has been primarily recruited for his ability to play at right wing-back as Ryan Strain recovers from hamstring surgery. However, he can operate across the defence or in midfield.
The versatile youngster spent last season on loan at Barrow, making 34 appearances for the league Two outfit.
And Stephenson’s rise has continued this term after earning a place in Arne Slot’s first-team group during pre-season, going on the club’s tour of the United States and lining up against Real Betis, Arsenal and Sevilla.
However, it has been decided that regular action will best serve his development and Stephenson, who started his career in the Sunderland academy, will follow in footsteps of ex-Dee Owen Beck by heading to Tayside on loan.
United boss Jim Goodwin told the club’s official website: “Luca is an exciting prospect who arrives at Tannadice with a fabulous pedigree, having spent the entirety of his youth career within an elite-level environment.
“His loan spell with Barrow last season was a burgeoning success. He played over 30 times across all competitions, proving his reliability and consistency within the senior game at such a young age.”
Quickfire debut
Stephenson, who was reportedly interesting Huddersfield and Wigan Athletic, will be eligible to make his debut in Sunday’s Premier Sports Cup last-16 clash with St Mirren pending SFA and international clearance.
He said: “I’m really looking forward to getting started up here. It’s a massive opportunity for me and the next step in my development. Playing in big fixtures, in front of massive crowds is exactly what I need to progress my career.”
Stephenson becomes United’s 12th new arrival following the captures of Dave Richards, Jack Walton, Vicko Sevelj, Ryan Strain, Will Ferry, David Babunski, Richard Odada, Kristijan Trapanovski, Jort van der Sande, Meshack Ubochioma and Emmanuel Adegoyega.
