The 22-year-old, who made five appearances for the Pilgrims during a successful loan spell in December and January, is now back at The Jakemans Stadium for a second stint.
Middleton signed for Harrogate in June 2017 following a season in the National League with North Ferriby.
He was also a member of Ferriby’s 2015/16 promotion-winning squad, who he joined after two seasons and seventy-four appearances at Scarborough Athletic.
Middleton previously spent time in the youth systems of both Doncaster Rovers and Hull City during his upbringing.
Middleton is eligible to feature against York City tomorrow but will not be able to face his parent club when the sides meet on Tuesday, April 17th.