The Millers, who won automatic promotion from League Two last year, have had a magnificent season but they saved one of their best performances for the most important night and prospered thanks to goals from Wes Thomas, Lee Frecklington and Kieran Agard.
It was a trademark display of attacking endeavour, orchestrated by the influential Ben Pringle, which could have yielded a bigger winning margin but was enough to set up a date at the home of football with Leyton Orient.
Simon Grayson's men more than played their part in an enthralling clash as they took the lead early on through Paul Gallagher's free-kick and then twice hit the woodwork in their attempts to get back into it though Jake King and Joe Garner.
But North End, who were among the pre-season favourites to go up, will now spend a fourth season in League One.
The tie was finely poised after Saturday's 1-1 first leg draw at Deepdale, but after a cagey opening the visitors seized the advantage in the 16th minute.
Rotherham defender Kari Arnason needlessly fouled Garner and from the resulting free-kick 30 yards out Gallagher's dangerous delivery evaded everyone, creeping into the far corner.
However, the Millers' response was swift and after Arnason should have atoned for his error almost immediately with a header that was superbly saved by Declan Rudd, they levelled in the 24th minute.
From a free-kick in a similar position to Preston's Pringle whipped in an equally delicious centre, which Thomas got a flying header to and it sailed through the hands of Rudd.
That quick riposte gave the Millers the impetus and again thanks to Pringle's incisive left foot they took the lead 10 minutes before the break.
The midfielder, who attracted interest from Reading earlier in the season, was afforded time and space on the left and sent in a pinpoint delivery which a late-arriving Frecklington superbly headed in off the post.
The game was now completely open and Preston had several chances to claw themselves level before the break, but Garner and Gallagher both shot over.
And the Millers' biggest escape came on the stroke of the interval, goalkeeper Adam Collin left to thank a higher power as he inexplicably allowed John Welsh's shot to slip through his grasp but he breathed a huge sigh of relief as it dropped just wide.
The see-saw nature of the clash continued into the second half and Pringle almost put his side further ahead, but his sweet volley crashed into the bar while North End's top scorer Garner went close to emulating his superb first-leg volley with an effort at the back post from Gallagher's cross which flew over.
After Gallagher wasted a free header from 12 yards the Millers put one foot on Wembley Way in the 67th minute thanks to Agard's 26th goal of the season.
But his strike owed much to the creativity of James Tavernier who foraged down the right, twisted David Buchanan inside and out and rolled the ball across for Agard to turn into the bottom corner.
Preston did not lie down as they desperately tried to mount a recovery, King's 35-yard effort clipping a defender on the way through and crashing into the upright before Garner endured a similar fate, as the Millers did enough to win.
Source : PA
Source: PA