The Wallabies prop has missed the last three matches with a knee injury, but comes straight back into McKellar's XV as part of an enforced reshuffle to the Brumbies' under-strength forward pack.
Harry Lloyd will make first start for the Brumbies at loosehead prop, while Academy graduates Fred Kaihea and Rory Scott are in line to make their Super Rugby debuts off the bench.
New recruit Sosefo Kautai has also been named as a substitute to cover Slipper, having only joined the Brumbies this week on a short-term contract.
In further team news, scrumhalf Nic White will wear the captain's armband with Allan Alaalatoa (suspension) and Tom Cusack (shoulder) unavailable for the round-six clash at Canberra Stadium.
McKellar was relieved to have Slipper back in action as the Brumbies brace for a major test of their front-row depth, with Scott Sio (elbow) and Tom Ross (knee) also out due to injury.
MORE CANBERRA SPORT
"He has a lot of experience at tighthead, he'll do the job for us there," McKellar said.
"There was relief. It's a tough position tighthead prop, probably the most important position on the field a lot of coaches will tell you.
"To have his experience back and not just from a scrum point of view, but in general play.
"Slips prides himself with his physicality and will certainly bring that, we'll need that on Friday."
Jahrome Brown will slot back into flanker to round out the changes to McKellar's XV, with local product Scott to cover the backrow.
McKellar said Scott, a Canberra Royals flanker, was ready to step up to Super Rugby AU level and was pleased to see another academy player promoted.
"It shows there's a genuine pathway to play Super Rugby here," McKellar said.
"He's a Marist boy, has played well for his club Royals over the last couple of years and just stood up in trials games. It'll be a proud moment."
Tom Wright, Bayley Kuenzle and Solomone Kata will likely be available for Friday week's clash with the NSW Waratahs in Sydney.
But until then, McKellar has confidence in the club's fringe players to fill the void in what "well and truly" looms as a test of depth.
"We've always said that and have full confidence in the guys who have got the opportunity this week," the Brumbies coach said.
"You're never going to win the competition using 15-23 players, you always have to go deep.
"We've had a bit of rough luck around injuries and suspensions, there's a cluster there in the front row. Thankfully we have good depth with the likes of Lloyd and Kaihea.
"They've worked closely with Dan Palmer around the scrum, and with Lord and me with the maul. They're ready to go."
SUPER RUGBY AU
Round six - Friday: ACT Brumbies v Western Force at Canberra Stadium, 7.45pm.
Brumbies team list: 1. Harry Lloyd, 2. Folau Fainga'a, 3. James Slipper, 4. Darcy Swain, 5. Cadeyrn Neville, 6. Rob Valentini, 7. Jahrome Brown, 8. Pete Samu, 9. Nic White (C), 10. Noah Lolesio, 11. Mack Hansen, 12. Irae Simone, 13. Len Ikitau, 14. Andy Muirhead, 15. Tom Banks. Replacements: 16. Lachlan Lonergan, 17. Fred Kaihea, 18. Sefo Kautai, 19. James Tucker, 20. Rory Scott, 21. Ryan Lonergan, 22. Reesjan Pasitoa, 23. Issak Fines-Leleiwasa.
Western Force team list: 1.Tom Robertson, 2. Feleti Kaitu'u, 3. Greg Holmes, 4. Jeremy Thrush, 5. Sitaleki Timani, 6. Fergus Lee Warner, 7. Kane Koteka, 8. Brynard Stander (c), 9. Tomas Cubelli, 10. Jack McIntrye, 11. Marcel Brache, 12. Henry Taefu, 13. Tevita Kuridrani, 14. Byron Ralston, 15. Jack McGregor. Replacements: 16. Jack Winchester, 17. Angus Wagner, 18. Santiago Medrano, 19. Ryan McCauley, 20. Tim Anstee, 21. Ian Prior, 22. Jono Lance, 23. Jordan Olowofela
Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: