Hitchock will stay on for the rest of the season after which his status and future as head coach of the Oilers will be re-evaluated, according to TSN's Darren Dreger.
The move comes after the Oilers lost six of their last seven games. They sit five points back of the final wild-card spot in the Western Conference and three points behind the Vancouver Canucks for third place in the Pacific Division.
McLellan concludes his Oilers tenure with a record of 123-119-24 in 266 games. The Oilers have struggled since reaching the second round of the playoffs during the 2016-17 campaign, posting a 45-50-7 record since then.
Hitchcock joins the team following a one-year stint with Dallas Stars last season that saw the veteran bench boss relieved of his duties after finishing three points out of a playoff spot with a 42-32-8 record.
The 66-year-old ranks third all-time in coaching wins with 823 victories during his 21-year career.
The Oilers are back in action on Tuesday when they take on the San Jose Sharks.