Birmingham are back in the Premier League at the first attempt after securing automatic promotion from the Championship with a 2-1 win at Reading on Sunday.
Alex McLeish's team had wasted a chance to seal promotion when they were beaten by Preston last weekend, but they made no mistake with their second and final opportunity on the last day of the season.
The Blues, who go up alongside champions Wolverhampton, went ahead through Keith Fahey's first half strike and Kevin Phillips put them within touching distance of the top-flight when he scored on the hour.
Marek Matejovsky reduced the deficit for Reading, who had an outside chance of automatic promotion themselves, a minute later but Birmingham held on to return to the Premier League a year after relegation.
McLeish said: "I'm really delighted for everyone at the club. Last week we wondered if our chance had gone and there were some tired legs out there.
"Before the match we just asked the lads to play the best game they've played all season.
"Now it is not the time to start talking about what we are going to do in the Premier League. We just need to savour this moment."
Birmingham went ahead in the 19th minute when Marcus Hahnemann allowed Fahey's shot to squirm through his grasp and over the line.
Former England international Phillips edged Birmingham closer to the promised land when he beat the offside trap and steered in a fine finish on the hour.
Although Matejovsky got one back for Reading a minute later with a low shot from the edge of the area, it wasn't enough to deny Birmingham.
Sheffield United could have gone up with a win if Birmingham had lost but they had to settle for third place and a play-off spot after being held to a goalless draw against Crystal Palace.
Former Blades boss Neil Warnock, now in charge of Palace, did no favours for his old club and their manager Kevin Blackwell, a long time assistant to Warnock, in a dour clash at Selhurst Park.
In the play-offs, United will play Preston, while Reading take on Burnley.
Cardiff started the final day in fifth but crashed out of the top six after losing 1-0 at Sheffield Wednesday, while Preston won 2-1 against QPR to pip the Welsh club.
Jermaine Johnson's stunning volley midway through the second half was enough to sink Cardiff, which opened the way for Sean St Ledger to score the 74th minute winner that sent Preston into the playoffs.
Preston finished level with Cardiff on 74 points with identical goal difference, but Alan Irvine's team, who beat Cardiff 6-0 last month, made it into the top six because they had scored one goal more than their rivals.
Norwich were relegated to the third tier of English football for the first time in 49 years after losing 4-2 against Charlton.
Bryan Gunn's team needed to win at the Valley and hope Barnsley lost at Plymouth to avoid the drop. In the event Barnsley won 2-1 at Plymouth, rendering Norwich's result irrelevant.
But Norwich showed no stomach for the fight as already-relegated Charlton tore them to shreds.
Nicky Bailey opened the scoring after nine minutes and when Deon Burton struck after 25 and 30 minutes Norwich's fate was sealed.
Alan Lee's goal gave Norwich a glimmer of hope but Burton completed his hat-trick in the second half. Sammy Clingan's strike was no consolation as the Canaries slumped into League One.
Elsewhere, Ipswich beat Coventry 2-1, Nottingham Forest defeated relegated Southampton 3-1, Waford won 3-1 against Derby and Wolverhampton beat Doncaster 1-0.