TOM Bradshaw's second-half goal was cancelled out by substitute Callum McManaman as Millwall's winless league run was extended to seven games.
Bradshaw put the Lions in front in the 60th minute before McManaman levelled with four minutes left.
Bart Bialkowski had twice denied James Collins, the second a superb save from the striker's 53rd-minute half-volley that was headed for the top corner.
Millwall took the lead when Jed Wallace's cross-shot was tipped away by goalkeeper Simon Sluga and Bradshaw slid the ball home at the back post.
But Luton substitutes Luke Bolton and McManaman combined to earn the hosts a point.
Bradshaw shows poacher's instinct
The opener was down to Millwall persistence as Ben Thompson kept in Bradshaw's cross before finding Wallace.
Bradshaw showed his goal instincts to react and tap in his third of the season. It was the first time Millwall had led away in the league this campaign. It was Bradshaw's first start since August 31 and he was full of energy and a running threat in behind the home defence.
Millwall were then a different attacking threat and Matt Smith had a glorious chance to make it 2-0 but headed Mahlon Romeo's cross wide from six yards out.
Thompson cracked an effort towards the top corner that Sluga tipped behind and in the last minute Jayson Molumby's 25-yard volley just cleared the crossbar.
Harris makes half-time tactical change
Having started in a 4-4-2 formation, Harris changed the shape of his side at the break to more match Luton and disrupt their midfield passing.
Thompson came on for Connor Mahoney, who hadn't been an attacking threat. Thompson went to the left of a narrow midfield three, with Molumby to the right of Ryan Leonard and Wallace in an advanced position.
Millwall were far more of an incisive attacking threat in the second period and will think they should have made the game safe. Smith will certainly be thinking about his header, though the cross came at him quickly.
Luton had faded but their substitutes gave them renewed attacking energy, and they deserved their point.
Ex-Lions midfielder impresses
Ryan Tunnicliffe kept things ticking along for Luton. He was in a narrow midfield with Izzy Brown moving into advanced areas.
Tunnicliffe could perhaps consider himself unlucky to have been released by Millwall in the summer. He didn't do a whole lot wrong in two seasons with the Lions, but midfield was an area Harris wanted to add to and Molumby looks a quality acquisition. The Ireland midfielder almost scored a spectacular late goal.
He'll naturally need more time to really flourish given this is his first season of regular senior league football. But there were hugely positive signs again at Kenilworth Road.
Tunnicliffe was announced as the man of the match, after being a key influence for his side.
Hatters dominate first half – but lack finishing touch
Luton were by far the more progressive side in the first half, passing crisply and with purpose.
Graeme Jones' side had chances to be ahead at the break. A rehearsed free-kick routine saw Pelly-Ruddock Mpanzu play a low ball across to Dan Potts whose rasping drive smacked off Smith.
In the 20th minute Potts raided down the left and his cross was probably hit with a bit too much pace for Harry Cornick arriving at the back post, and the ball hit the forward and rebounded away from goal.
Bialkowski saved Collins' flick and late in the half Tunnicliffe cut in on the left side of the box but his shot was deflected up in the air before the offside flag went up.
There were four changes from the 1-1 draw at Huddersfield. Shaun Hutchinson was captain with Alex Pearce on the bench.
Murray Wallace replaced the suspended Shane Ferguson, and Molumby returned for Shaun Williams.
Harris switched to 4-4-2 as Bradshaw came in for Aiden O'Brien to partner Smith up front.
Millwall: 4-4-2: Bialkowski; Romeo, Hutchinson, Cooper, M Wallace; J Wallace, Molumby, Leonard, Mahoney (Mahoney, 46); Bradshaw, Smith (O'Brien, 82).
Subs: Steele, McCarthy, Williams, Bodvarsson, Pearce.
Image: Millwall FC