Roff, who won 86 caps and scored 30 Test tries for the Wallabies, lines up in Oxford's midfield when they attempt to avenge a 31-16 thumping against Cambridge last year - the Dark Blues' biggest Varsity Match defeat since 1996.
And the 31-year-old student of politics, philosophy and economics is pivotal to Oxford's hopes in a side containing six survivors from a year ago.
Roff said: "You speak to anyone who knows about this game, and they know about the tradition of it, the rivalry and the history.
"To be able to say you have been a part of it - it is one of the great boxes to tick in rugby - and the opportunity to do that is fantastic.
"It will be nice to be at Twickenham to have half the home ground behind me, rather than it being a hostile away ground, as it has been for most of the times I have played here.
"There is a significant focus on this one game, but the season and the journey has been fantastic with this Oxford team, and the bonds you have with the guys make it special when you run out."
Roff will line up at outside centre, rather than in his more familiar positions of wing or full-back, and his experience - together with expertise provided by Dark Blues skipper and former London Irish scrum-half Kevin Brennan - are crucial to Oxford's cause.
"I spoke to Kevin about wanting to get more involved," added Roff.
"At times, on the wing and at full-back, you have to manufacture your own involvement, but at 13 you are in the game both in attack and defence.
"Some of the others guys in the team say I am slowing down and getting nearer the scrum - which might be a fair assessment as well! - but we have a good back three, and I want to be able to help them.
"It is a matter of trying to get the guys up to the maximum level they can perform at. That is the challenge in a university side."
Roff, who already has a bachelor of applied finance degree from the University of Southern Queensland, admits his studies in England have proved a real eye-opener.
He said: "Unfortunately, academically I have to do a fair bit more than the young, bright kids.
"My average day involves lectures and one-on-one tutorials which I have found as daunting and nerve-wracking as any Test match I have played in.
"To sit in a room discussing a topic one-on-one with someone who is obviously an expert in their field is quite daunting.
"Then there is the outside study. It is an environment in which you can learn as much as you are willing to put in.
"The days are taken up with doing that, and then you have the rugby aspect most evenings. Then there is the social side of things, trying to keep up with the young students.
"They seem to want to look after me, which is a sad indictment. I have taken the average age of the team up about five years I think!"
And as for life after university, Roff added: "I am an atypical student in that I just don't know!
"It is probably all right for a 19-year-old, but I am 31 with a pregnant wife at home, and I am supposed to have some direction.
"I think I will step away from rugby and make a clean break and go into something else. But I am not sure what that is."
While Oxford hope Roff can work some magic for them tomorrow, Cambridge have their own key 'thirtysomething' in fly-half Jon Ufton, the former Wasps back who makes a fourth Varsity Match appearance.
The Light Blues can also call on wing David Akinluyi, a try-scorer last season who was then snapped up by Northampton, while New Zealander John Blaikie emulates his brother Duncan in captaining Cambridge at Twickenham.
Cambridge lead the 124-game series 58-52, with 14 draws.