Dr. Waller previously spent four years at the club as first-team doctor before departing to become Head of Medicine at Leicester City last summer.
The 65-year-old formed a strong bond with current first-team Manager Michael Beale during his previous time at Ibrox, playing an integral role in guiding the club safely through the Covid-19 pandemic.
Dr. Waller spent 17 years at Liverpool, forming a close alliance with Gerard Houllier, before returning to work with the Frenchman at Aston Villa following a brief stint as Medical Director in the United Arab Emirates.
The highly experienced Waller also counts Hull City and England Under-21s among his former posts, and he returns to the club ahead of a pivotal pre-season for the squad.
Following his appointment, Waller commented: “I am delighted to return to Rangers as Director of Medical and Performance.
“This club holds a special place in my heart after the journey we embarked on as a team back in 2018, and I look forward to working closely with the manager and the entire backroom team as we continue our preparations for what promises to be an exciting campaign.
“The responsibility that I feel to serve as Director of Medical and Performance at this great club is immense, and I am hugely optimistic about what the future holds both on and off the pitch.”