The goalkeeper was a doubt for the match having suffered viral meningitis, but took his place in the team and made two brave blocks to keep QPR out.
Marshall was easily Millwall's best player as they struggled to break down a resolute Rangers defence and without his stops the west Londoners would have left the Den with all three points.
The first-half was abysmal viewing as both sides resorted to long aimless balls upfield to no effect. There were barely a dozen decent passes in the entire 45 minutes and, unsurprisingly, goalscoring chances were thin on the ground.
However, Paul Furlong could have given QPR the perfect start before the match fell into the mire.
He got in behind the Millwall defence from a George Santos through-ball and went one-on-one with Marshall. The Lions goalkeeper narrowed the angle quickly and made a brave block as Furlong struck his shot towards the net.
But that was as exciting as it got as the match turned into a mind-numbing midfield battle, with Barry Hayles and Santos going into the book for over-enthusiastic tackles.
At least things got better after the break, although they could hardly have got worse.
First Furlong had a goalbound shot deflected over the bar and from the resulting corner Danny Dichio had to make a fearless block from Danny Shittu's powerful half-volley.
QPR piled on the pressure and Furlong fired a sweet shot into the side-netting from just outside the box before sub Tony Thorpe was presented with a great chance as defender Darren Ward dallied.
The striker raced into the area, but once again Marshall reacted quickly to come off his line and make another smart save.
Millwall responded and Alan Dunne should have done better with a half-volley from inside the area, but instead skewed his shot well wide of the post.
The improvement in the play also saw a drastic reduction in the number of fouls as both sets of players concentrated on scoring a goal rather than kicking their opposite number. Even so, Richard Edghill's name was taken by referee Phil Crossley after he brought down David Livermore.
QPR continued to dominate and Furlong should have scored, but somehow steered the ball wide from just six yards after a precision cross by sub Martin Rowlands.
Lee Cook then appealed for a penalty after a challenge by Mark Phillips, but the ref was unimpressed and QPR were left to settle for a point.