Todorov settled the jangling nerves of the 19,221 crowd in the 73rd minute with his 20th goal of the season as Portsmouth returned to the top-flight for the first time since 1988.
Midfielder Nigel Quashie was the provider as he drilled a low cross to the Bulgarian who was unmarked at the far post.
Todorov met the centre with a firm right-footed shot which Nik Michopoulos did well to get both hands on, but could not prevent the ball going over the line much to the delight of the home crowd.
Pompey's supporters greeted the final whistle by streaming on to the pitch to celebrate their promotion and Harry Redknapp's side made a triumphant lap of honour soon after.
But Redknapp and his players were forced to endure a nervous evening as they searched for the victory that they needed to ensure them of a place in the top two.
Captain Paul Merson wasted a golden chance in the 13th minute after Burnley defender Dean West had needlessly fouled Gianluca Festa in the area.
But the former England midfielder blasted his spot-kick against the underside of the bar and Mark McGregor blocked Lee Bradbury's follow-up.
Burnley were only threatening on the counter attack and it was Portsmouth who continued to spurn chance after chance to take a grip on the game.
Bradbury was unable to take advantage of a poor back header from Graham Branch five minutes from half time and the striker wasted an even better opportunity just seconds later when he blazed over with just the keeper to beat.
Michopoulos kept Portsmouth at bay after the restart with fine saves to deny Bradbury, Quashie and Todorov and it looked as if the home side would never score before Todorov finally broke the deadlock.
Burnley's best chance came in the 67th minute when Robbie Blake released striker Gareth Taylor, but he pulled his left-foot shot wide with just Shaka Hislop to beat and Portsmouth clung on to launch a night of celebration.