Steve Evans' side are one win away from securing back-to-back promotions following Thursday's 3-1 second-leg triumph, which gave them a 4-2 aggregate success in their League One play-off semi-final.
Preston, who have now failed in all nine of their play-off campaigns, led at the New York Stadium through Paul Gallagher's fortuitous opener, but the hosts hit back in style.
Ben Pringle set up Wes Thomas and Lee Frecklington before the break, with Kieran Agard's strike settling it after the interval.
The visitors, who needed a stunning strike from Joe Garner to ensure they went into the second leg level, went ahead when Gallagher's 16th-minute free-kick eluded everyone and deceived Rotherham goalkeeper Adam Collin as it bounced into the left-hand corner of his goal.
But Rotherham's response was impressive, Thomas heading home Pringle's set-piece delivery eight minutes later.
Pringle was the provider for Frecklington's goal just past the half-hour mark, too, as Evans' charges seized the initiative.
Gallagher missed an excellent headed chance early in the second half as Preston sought a way back into the match, only for Agard put it beyond doubt with a close-range finish after 67 minutes.
Simon Grayson's side struck the post twice in the final 15 minutes as Rotherham moved closer to a second-tier return after a nine-year absence.
