But the former Edinburgh player recognises the opportunity has only arisen after friend, Chris Cusiter, suffered injury misery in the win over the Pacific Islanders last week.
The Lions international has undergone shoulder surgery this week after landing awkwardly during the game on Saturday and is expected to be out for up to four months.
Lawson said: "I really feel for Chris. He is a good mate of mine and the way it happened as well has made it that much harder to stomach, but it has presented me with an opportunity.
"Chris' misfortune has opened this door. I didn't really think it would happen so soon.
"He sent me a text earlier in the week saying he hoped I would get the nod, and I am delighted that has been the case."
Meanwhile, Lawson has been receiving specialist tutelage from former Scotland captain Bryan Redpath since moving to Gloucester in the summer.
And the scrum-half insists that help has been crucial to his development as a player.
Lawson added: "I think my game has developed since I moved to Gloucester.
"It is the first time I have been coached by a scrum-half, and having him down there has developed me, whether it is just awareness on the pitch or the development of a few skills.
"The Guinness Premiership is different from the Magners League in a number of ways, and, having had exposure to that educates you and gives you the opportunity to learn."
Lawson will not be the only debutant against the Wallabies with Edinburgh flanker Alasdair Strokosch also on the bench.
The 23-year-old was withdrawn from the Scotland A team to play Australia A at McDiarmid Park on Tuesday after Johnnie Beattie was ruled out with an ankle injury.
Now Strokosch has vowed to prove himself worthy of a place in the squad to head coach Frank Hadden.
He said: "I am really up for it. I can't wait to get out there and go mental.
"It feels good just to be in the squad. Playing for Scotland is the sort of thing you dream about when you are a little boy and it is getting pretty close now.
"It is a big opportunity and I need to make sure I take it.
"I need to prove I can be good at this level, and prove to Frank I belong in the squad."
But Strokosch has also credited a heart-to-heart with former New Zealand international Todd Blackadder for his emergence as an international prospect.
Blackadder succeeded Hadden as interim head coach at Edinburgh last season before returning to his homeland this summer.
Strokosch said: "Last season I spoke to Todd about my game and he told me all I needed to do if I was going to realise my potential is be confident and have faith in my own ability.
"He reminded me I was still young and assured me my time would come.
"Then, towards the end of last season, I got a run of games for Edinburgh, made it into the Scotland A squad for the Churchill Cup during the summer, and I've been playing regularly for Edinburgh ever since.
"Confidence has been the biggest thing in me being able to do that."