Kellaway will move to outside centre to cover the loss of suspended Ray Nu'u as the Rebels look to earn a third successive win after a horror start to the season.
The Reds, meanwhile, are coming off the bye and also gunning for a third straight victory with their last match a rousing win over the Brumbies.
They will have former Wallabies captain, hooker Stephen Moore travelling to Melbourne as surprise injury cover.
The 39-year-old retired from professional rugby in 2017 but has kept playing club rugby in Brisbane.
Rebels attack coach Ryan Martin said Kellaway would bring some special qualities to his new role.
Englishman George Worth gets his first start of the year on the wing.
"Bringing him into centre this week adds a real intelligence, and we can maybe play a little bit differently, manipulate a lot more," Martin said of Kellaway, who has played in the UK, Japan and New Zealand.
"I think it's exciting for him - he's actually been a successful centre in the past so it just means he's going to get a little bit more contact with a ball and gets to be organising in the D (defensive) line a lot more."
Making his first appearance of the season after ongoing hamstring issues, Reds winger Suliasi Vunivalu will command plenty of attention at his former NRL ground, AAMI Park.
Kellaway's centre partner Stacey Ili said they couldn't afford to focus on the ex-Storm flyer given the threat of the entire Reds back three, including Filipo Daugunu and Jordan Petaia.
"Their whole back three is dangerous and when they get the ball you don't know what they're going to do with it," Ili said.
"We'll put an emphasis on limiting their opportunities but we're definitely wary of Suli."
Melbourne are hosting "Super Round" next weekend, with their entire round being played at AAMI Park and the trans-Tasman component of the competition kicking off.
The Rebels are up against the Crusaders next Sunday, while they have games looming against the Blues and Moana Pasifika.
Ili said the Reds would be a litmus test ahead of those games.
"The Reds definitely they kind of play the same brand as the New Zealanders so it's good for us to get a taste of it before they all come over," Ili said.
"We've got a tough run in coming weeks but we're looking forward to it."
