The Lions dominated the possession from the off in Saturday's Championship clash and their best chance came with 15 minutes gone when McQuoid somehow managed to fire wide from two yards out.
Jimmy Abdou also had a shot saved by Barnsley goalkeeper Luke Steele and in the second half Paul Robinson just failed to get a telling touch on Hameur Bouazza's free-kick.
Barnsley lacked any real ambition but managed to hold on for a point to build on their first win of the season at Reading last weekend.
Millwall made a good start and James Henry's corner found Darius Henderson but his header was saved by Steele.
With 15 minutes gone the Lions should have gone in front when Henderson fired across goal from Bouazza's knock down and the onrushing McQuoid put the ball wide with the goal gaping.
The home side continued to press forward but Barnsley were restricting them to long range efforts and Bouazza fired wide from 35 yards before Tamika Mkandawire tried his luck from 30 yards, but Steele was untroubled.
Barnsley were putting men behind the ball and Millwall struggled to break them down with McQuoid having a hopeful shot blocked by Rob Edwards.
Seven minutes before half-time they did get through when Abdou broke clear but his shot was superbly parried away by Steele.
Barnsley began to show a little bit more adventure at the start of the second half and it almost paid dividends when the ball broke to Daniel Drinkwater but his shot from the edge of the box was blocked by Mkandawire.
That let-off woke Millwall up and Henry ran at the Barnsley defence before letting fly with an effort from 25 yards which dipped just over the bar.
Millwall once again began to probe in search of an opener, but just as in the first half, Barnsley closed ranks and got men behind the ball to stop the home side playing.
Just after the hour mark Bouazza whipped in a free-kick and in a goalmouth scramble Henderson saw a shot saved by Steele but the visitors managed to survive.
The Lions could have been forgiven for thinking it was not going to be their day with 15 minutes remaining when a superb free-kick from Bouazza left Steele rooted to the spot and Robinson failed to get a crucial touch on the ball.
Moments later substitute John Marquis had a shot deflected wide as the Lions turned up the heat on the Barnsley defence, but they were unable to find a way through.