Macken struck in the 96th minute to give Barsnley a deserved victory they could have wrapped up in the first half - and extend the worst start to a season in Ipswich's history.
The Tractor Boys trailed after only eight minutes to Iain Hume's strike, and the Tykes continued to dominate.
However Liam Rosenior capitalised on a goalkeeper error to equalise on half-time, and Hume missed a late penalty as Ipswich appeared destined for a point.
They even had their chances to pick up all three points in five minutes of added time, as did Barnsley, but it was Macken who grabbed the goal when Ipswich failed to clear a free-kick.
Ipswich were unchanged from the side that drew 3-3 at Sheffield United in midweek, and their luck had not changed either as they went behind to another early goal.
Hume shrugged off two defenders before firing a low shot beyond the reach of Richard Wright.
With swirling winds inside Oakwell making this a perilous day for the goalkeepers, Ipswich almost got a goal out of nothing in the 18th minute when Barosz Bialkowski lost the flight of Grant Leadbitter's free-kick, almost allowing Tommy Smith to latch on to the end of it.
Hume continued to torment Ipswich, almost grabbing a second when he met Jamal Campbell-Ryce's cross but, surrounded by defenders, he was forced to settle for a corner.
The striker took it himself, finding Stephen Foster who sent a bullet header skimming off the top of the crossbar.
Ipswich were going to need a Barnsley mistake to score and they got one with 10 minutes left in the half when Foster inexplicably let Tomas Priskin's cross roll past him, unaware that Alan Quinn was ready to pounce, but the defender recovered to block the shot.
Priskin had a great chance to level moments later, pulling off his marker to meet Jon Walters' cross, but his header was weak.
The Tykes had dominated the half and should have added to their lead, but instead, Barnsley gave Ipswich another chance as Bialkowski's torrid afternoon took another turn of the worse.
Moments after being on the receiving end of a crunching tackle from Priskin, he flapped at Grant Leadbitter's powerful free-kick, and Rosenior headed in the rebound.
The game turned feisty in the second half with few chances at either end.
Macken should have put Barnsley back in front just before the hour mark when Ryan Shotton's long throw found him only a couple of yards out but he poked his shot wide.
At the other end, Walter's flick gave Carlos Edwards a great chance but he fluffed his shot terribly. Liam Trotter then wasted another good chance when Walter's cross found him all alone on the edge of the area, but he fired over.
Ipswich were playing with more confidence, and Bialkowski had to be alert to gather Rosenior's dangerous cross with several players lurking.
There was then drama at the other end where referee Phil Gibbs harshly gave a penalty for a foul off the ball by Smith on Hume, but the Barnsley striker saw his spot-kick crash back off the upright.
As normal time ended, McAuley stabbed a shot through a crowded penalty area which Bialkowski scrambled away, while Shotton fluffed a similar chance before Macken's killer blow.