Fairbanks, who missed last weekend's match through injury, will partner Adam Ashley-Cooper in the centres, forming a new midfield partnership from the one that defeated the Sharks in Durban last weekend.
Fairbanks says he is ready to return against the Lions.
"I had some lingering pain and stiffness in my neck and down my shoulder," he said. "But fortunately I've had physio on it over the past week or so and it feels fine now."
"While it was frustrating to sit on the sideline last weekend, it was great to see the team play so well and it definitely helps coming back into a side that is playing with a lot of confidence."
Brumbies had coach Laurie Fisher says he had little hesitation in naming Fairbanks in his starting line-up.
"Gene's played well for us all year and he certainly deserves the opportunity to come back into the side," he said. "His defence has been magnificent for us this year and deciding whether or not he should come back into the starting line-up wasn't a difficult choice to make."
Fairbanks replaces Julian Huxley, who has been named at fullback, while Peter Playford shifts from outside centre to the reserves list. Playford is joined by front-rower John Ulugia as the only additions to the Brumbies' bench.
Fisher, who has named an unchanged forward pack from last round, says his side is wary of a Lions outfit that defeated the Hurricanes 30-7 last weekend.
"The Lions have a very young squad that performed very well in the Currie Cup under [Lions head coach] Eugene Eloff," he said. "They've been developing and have picked an enthusiastic squad that plays with a lot of passion which is three-quarters of the battle. They're a really, really dangerous side.
"What we're focusing on is making sure that our concentration and preparation is the equal of last week. The key for us is that we don't let ourselves down by not preparing at 100 percent and by not being as thorough as we could be. But indications so far are that the guys are very, very keen and training this week has been very good, so we're definitely looking at putting our best foot forward on Saturday night."
Brumbies: 15 Julian Huxley, 14 Clyde Rathbone, 13 Adam Ashley-Cooper, 12 Gene Fairbanks, 11 Mark Gerrard, 10 Stephen Larkham, 9 George Gregan, 8 Stephen Hoiles, 7 George Smith (c), 6 Jone Tawake, 5 Mark Chisholm, 4 Adam Wallace-Harrison, 3 Guy Shepherdson, 2 Jeremy Paul, 1 Nic Henderson
Replacements: 16 Saia Faingaa, 17 John Ulugia, 18 Richard Stanford, 19 Julian Salvi, 20 Patrick Phibbs, 21 Peter Playford, 22 Francis Fainifo
Date: Saturday 31 March 2007
Venue: Ellis Park, Johannesburg
Kick-off: 17.00 (15.00 GMT)
Referee: Paul Honiss (New Zealand)
Touch judges: Bryce Lawrence (New Zealand), JC Fortuin
Television match official: Johann Meuwesen (South Africa)
Assessor: Arrie Schoonwinkel (South Africa), Sandy MacNeill (Australia)