Robinson met a Greg Cunningham cross in the 80th minute, chesting the ball over the line from four yards in front of PNE's large travelling support.
North End had trailed to an Aiden O'Brien goal two minutes before half-time, that having come slightly against the run of play after the visitors had certainly enjoyed the better of the opening 30 minutes.
In the second half, Alex Neil's men had struggled to break down a solid home side as the game turned into something of a battle.
But helped by a couple of changes, the gaps started to appear and Robinson levelled to earn a point which was probably a fair result.
The North End line-up had shown five changes from the side which had won at Wycombe in the FA Cup.
Chris Maxwell, Ben Davies, Ben Pearson and Jordan Hugill all returned after being rested last week, with Billy Bodin retaining his place to make his Championship debut.
Injury ruled out Paul Huntington and Calum Woods, which meant a game in the centre of defence for Tom Clarke alongside Davies.
Alan Browne played in an unfamiliar right-back role in the absence of Woods and Darnell Fisher.
PNE enjoyed a decent first half hour, playing a possession-based game with Paul Gallagher often dropping deep to get the ball short from Maxwell and build play from there.
Robinson tested Lions keeper Jordan Archer with a shot from 25 yards, Archer diving to parry rather unconvincingly.
Bodin saw a shot blocked by the sliding James Meredith, the interception taking the ball behind for a corner,
In the 33rd minute, Robinson picked up possession 35 yards out and turned towards goal, eventually getting a shot away which bounced wide.
Millwall started to find their way into the game as the interval approached,, Ryan Tunnicliffe volleying wide of the target after a corner had been headed out of the Preston box.
Steve Morison met a free-kick beyond the far post and sent a header across the six-yard box and wide.
The home side took the lead in the 43rd minute, North End switching off after conceding a throw-in on their left side.
Jed Wallace was afforded too much space to send a low cross into the middle which O'Brien spun to steer a shot into the bottom corner.
At the break Tom Barkhuizen replaced Bodin, slotting in on the right hand side of Preston's attack.
With 14 minutes of the second half played, Millwall's George Saville fired a shot from outside the box wide - that coming shortly after Ben Pearson had been booked.
Although they saw plenty of the ball, North End found it hard to play their way through the solid home ranks. some of their approach work a bit predictable.
Paul Gallagher curled a shot from 20 yards into the keeper's gloves as the visitors began to look a bit more threatening.
Daryl Horgan came on in place on Josh Harop in the 70th minute, the winger going close five minutes later with a shot from outside the box which clipped a Millwall boot and went behind.
North End's third substitute saw Daniel Johnson replace Pearson, that change having almost taken place inside the first 15 minutes when Pearson got an injury.
Within a couple of minutes of that final change, Preston were level.
Johnson slid a pass down the left to play Cunningham into space, the full-back surging forward and driving a cross into the middle where Robinson lunged forward to direct the ball ijnto the net with his chest.
Cunningham set up another chance soon after, his cross finding Horgan at the far post who took too long to bring it under control and saw his shot blocked.
Millwall: Archer, Romeo, Hutchinson, Cooper, Meredith, Wallace (Onyedinma 88), Tunnicliffe, Saville, O'Brien, Morison, Gregory (Williams 88). Subs (not used): McLaughlin, Craig, Thompson, Elliott, Martin.
PNE: Browne, Browne, Clarke, Davies, Cunningham, Pearson (Johnson 78), Gallagher, Bodin (Barkhuizen 46), Harrop (Horgan 70), Robinson, Hugill. Subs (not used): Boyle, Welsh, O'Connor, Rudd.
Referee: Jeremy Simpson (Carnforth)
Attendance: 11,751 (1,483 PNE)