The 21-year-old has made three RaboDirect PRO12 starts for the Ulstermen, including a try-scoring appearance against Connacht, and his Heineken Cup debut followed against Castres Olympique when he memorably put Ruan Pienaar away for the bonus point try.
The busy blonde-topped centre has quickly come under the radar of Declan Kidney and his fellow coaches, with Les Kiss offering an insight recently into what the youngster offers.
"He can pass the ball well, he can pass short and long. He has good footwork, and as Gert (Smal) and I recognised often from when we've gone up to watch Ulster play or train, he carries his body weight well," explained Kiss.
"Luke is a good solid lad, plus his agility is nice. Usually when we talk about agility, it is in attack but his agility in defence is very good too.
"He can actually shape his defence to handle any threat coming in a direct sense but also if the ball shifts wide he can move off that channel and get into a defensive channel wider quite quickly. So across those broad skill sets, he's shown some promise."
Now the former Ireland Under-20 international will get his first chance to show those skills against a senior international team with Fiji providing the opposition in Saturday's non-cap international.
Marshall is one of three uncapped players in the Ireland XV back-line alongside his Ulster colleagues Craig Gilroy and Paddy Jackson, with another northern ace, Darren Cave, adding some experience at outside centre.
His ability to step into the out-half role could come in handy as Marshall and Jackson look to direct matters against the tourists.
"I'm quite happy that the first time I'm playing for Ireland will be alongside Paddy. I've known him for quite a few years. We think the same way and we instinctively know what the other is going to do," admitted Marshall.
"I like to get my hands on the ball and help the out-half make a few decisions, take the heat off the out-half."
The Ballymena clubman has enjoyed his first few weeks in the Ireland camp, agreeing with Jackson that the food, in particular, has been of a top notch variety.
The laidback Jackson drew quite a few laughs at the team announcement press conference when stating: "It's all quite new to us, but I like the food. Whenever you want, you can go and have a wee munch."
Marshall is likely to need all of his 15 stone bulk to stop Leicester powerhouse Vereniki Goneva in the Fijian midfield, while also hoping to use his own impressive footwork and strength to unlock the visitors' defence.
"I'm very excited and I can't wait to get on the pitch. When you start playing rugby, you want to play for your country," he commented.
"On the physical side, you look forward to meeting traffic, you want the physical confrontation. Hopefully if the opponent is bigger, I'll be able to get around him and make a few breaks."