The livewire scrum-half has been referred to as 'wee Marshy' for so long that his emergence in this new role creates a challenge for all concerned. But tonight, with so many of Ulster's first-choice back-line troops missing, he knows he has to lead by example.
"With the number of backs we have down in Dublin and some of the injuries we've had over the past few weeks it means I'm one of the older guys, so it's important that I do my job properly and try to encourage the help the others, too, particularly when they're maybe getting their first game for a while," is how he describes the situation.
The player who partners him tonight at half-back, James McKinney, is one such an example.
"We've played a bit and obviously you're making different reps in training. We always try to rotate the scrum-halves and out-halves in training just to try and keep that fresh so while we haven't played a lot together we have played a bit," Marshall explains.
"I like the way he plays so hopefully we can put in a good performance and get the team going because obviously it's such an important axis in terms of the whole team's performance."
He knows the period between the autumn internationals and the start of the Six Nations is a key part of the season. After tonight's date with Edinburgh, Ulster have a run of four matches against Italian opponents – Zebre away, Benetton Treviso home and away and Zebre at home – with the middle two of that quartet being Heineken Cup dates.
"I think the next month is massive in terms of the two Rabo games followed by the two Heineken games," Marshall says.
"Obviously we want to be involved and challenging in both those competitions so that means picking up results in the next few weeks.
"It's important for us being at home, against Edinburgh, that we go out and get a result. Yes, we want a great performance, but at the end of the day we'll take any sort of a win over the next few weeks to make sure that we're in or close to the top four bracket of the league and still in pole position in our group in Europe."
Asked about the timing of the three-week break in the wake of having lost to Scarlets on November 2, he replies: "I think sometimes you get a bit of momentum and we'd won six on the bounce. If we'd won that Scarlets game, we probably wouldn't have wanted the break to come along at that stage.
"But after losing and not performing that well, it probably came at an okay time for us. It gave guys a chance to rest their bodies for a week, and guys who'd been carrying knocks have had a bit of rest as well.
"Hopefully we'll see an increased performance now that we've had a bit of time away and are itching to get back out on the pitch."
Marshall admits that players not being available sometimes creates problems.
"It can be a wee bit frustrating at times whenever guys are here, there and everywhere, but it's the same for all teams. We're no different or no worse off than anybody else," he points out.
"We just need to worry about what we can control and that's our own environment here at Ulster. If guys get selected for international duty we're delighted for them. We don't resent them being away or anything like that.
"It just means other guys are going to get opportunities this week or next week and it's important they realise that and grasp it with both hands.
"Sometimes you only get one or two chances to try and make a name for yourself or stamp your authority on a game, so it's important for these guys coming through that they put on the Ulster jersey with pride and play with passion that everybody can see.
"We never know if we'll be getting any of the international players back, so we prepare for them not being available using what we've got here. That's all we can do.
"If we get somebody back, great, that'll be a boost for everyone. But we know not to expect that."
Marshall expects tonight's opponents to be well organised and direct.
"I know Solly (Edinburgh coach Alan Solomons) having worked with him at Belfast Harlequins and he's meticulous in terms of attention to detail, so I'd say they'll be very well drilled and probably even more physical than they have been over the past year or two.
"We know we need to front. We need our forwards to get into their set-piece and try to disrupt it; we need our backs to be clinical when we're striking.
"We know that if we put everything together we can be a formidable side, but we also know that – like any team – if we don't perform we're vulnerable."