MILLWALL are through to the League One play-off final where they will meet Barnsley at Wembley on Sunday week for a place in the Championship.
Lee Gregory put Millwall ahead with his 27th goal of the season but Bradford responded and equalised before half-time through striker Jamie Proctor.
The Bantams pressed to reduce the deficit in the second half but Millwall were relatively comfortable and reached their first play-off final since 2010.
Bradford were first to threaten when Steve Morison had to head away Tony McMahon's cross at the back post.
In the 17th minute Gregory led a breakaway and held the ball up to play Ben Thompson into the box. But Josh Cullen had made the long run back to track to midfielder and block his shot.
Millwall went ahead in the 34th minute when just after Nathan Clarke had headed McMahon's corner wide, Morison showed deft footwork and dragged in a couple of defenders before squaring for Gregory who drilled home a low shot from just outside the box.
Six minutes before the break Joe Martin almost repeated the goal he scored in the first leg but from his free-kick Ben Williams tipped the ball over the crossbar.
Bradford were three goals behind in the tie but pulled one back when Kyel Reid beat Carlos Edwards to pick out Proctor. The striker's initial shot was saved by Jordan Archer but Proctor reacted quickest to slam home the equaliser.
Jimmy Abdou had the chance to increase Millwall's lead but fired well over from a good position in the box after Rory McArdle's clearing header had fallen to him.
In the 54th minute Byron Webster met Chris Taylor's corner but couldn't direct his header on target.
Bradford thought they could have had a penalty in the 72nd minute when substitute Tom Thopre burst into the box and fell under Mark Beevers' challenge but referee Tim Robinson indicated the defender had won the ball.
Bradford brought on Steven Davies for more attacking impetus but Archer was rarely troubled.
Millwall don't hold back
Any suspicions Millwall would sit on their two-goal lead were banished from the first whistle. Neil Harris' side pressed high up the pitch to put their opponents under pressure in the early stages.
At the back Webster and Beevers picked up where they had left off at Valley Parade but the worry was always the lack of pace in Edwards' 37-year-old legs against the more sprightly Reid.
That eventually directly led to Bradford's equaliser but it was Edwards' positional sense that prevented the Lions falling behind just before half-time. It was Proctor again doing the damage when he raced in behind Millwall's defence. He played the ball across the box towards Reid but Edwards stretched to just flick the ball off the winger's toe.
At the other end Morison and Gregory were involved in another ferocious physical battle with Clarke and McArdle. But it was the strikers' more subtle strengths that led to the opening goal.
In the first 10 minutes the home crowd had wanted two penalties when Shane Ferguson's cross appeared to hit Stephen Darby's arm and then Abdou went down under a challenge in the box.
That Proctor goal should have been the catalyst for a Bradford onslaught after the break, but though they dominated possession and territory they never really looked like they were capable of prising Millwall open.
Man of the match
This was arguably Abdou's best performance of the season. He was everywhere for Millwall and made so many vital contributions. Yes, he should have scored but then in the 77th minute he did what he does so well and tracked Lee Evans' run and flicked the ball back to Archer.
Moments before that he had been bent over trying to get his breadth back after so much work.
In the second period he also had to be aware of Reid's threat against Edwards and with 10 minutes to go it was clear how much he was feeling the effort he had put in. Yet still he found some reserve of energy to help Martin deal with Proctor on the other side of the pitch as Bradford, with three strikers, sought a second goal.
Gregory and Morison were also locked into a constant physical fight and never gave in, while Webster was immense at the back.
It's going to be a frenetic week.
There was already a bigger media presence at Calmont Road before the play-offs and that will only increase. The challenge for Millwall is to manage it and retain focus.
Barnsley easily beat Walsall, physically dominating them in a way they won't be able to do to Millwall.
The Tykes have defeated Millwall twice this season but strong cases could be made the Lions should have at least drawn the first and won the second after a number of spurned chances.
Millwall are likely to have just four of the players that started in the 3-2 defeat to Barnsley in August, though their final opponents have also used the loan market well recruiting the likes of Josh Brownhill and Ashley Fletcher.
The big advantage for Barnsley is they've gone through this whole routine already this season after their Johnstone's Paint Trophy final win over Oxford at Wembley.
They will have the benefits of repeating their logistics, little will be new for them apart from the heightened pressure.
A lot will be depend on how Millwall players react to the occasion, but Harris, David Forde, Tony Craig and Abdou all experienced the contrasting emotions of 2009 and 2010 and the lessons that were absorbed.
Some players admitted after defeating Leeds in the semi-final in 2009 they took Scunthorpe for granted.
That won't be the case this time, with those two defeats to Barnsley a reminder of the challenge they face.
There was another pitch invasion at the final whistle on Friday night – but Harris will enforce the message to his players the job is not yet complete.