After both West Brom and Brentford were beaten at the weekend, the Baggies only needed to match the third-placed side's result to seal a return to the Premier League after two seasons away in England's second tier.
A seemingly straightforward home fixture against QPR did not go entirely to plan for West Brom, but a 2-2 draw took them up as Brentford went down 2-1 to Barnsley on Wednesday.
That result saw Barnsley stay up, but Wigan could not join them as they drew 1-1 with Fulham – who could have been promoted with a win – and went down due to a looming 12-point deduction.
Charlton Athletic and Hull City were also demoted, while there was a similarly chaotic finish in the play-off race.
BAGGIES BEST BRENTFORD
Both West Brom and Brentford lost their nerve with two matches of the campaign remaining, but a return of just a single point from a pair of games proved enough for Slaven Bilic's team.
West Brom trailed to Ryan Manning's strike before turning the match on its head with goals either side of half-time through Grady Diangana and Callum Robinson, only for Eberechi Eze to equalise just past the hour-mark.
It mattered not, though, as Brentford failed to capitalise, instead losing again.
Josh Dasilva cancelled out Callum Styles' Barnsley opener, but as Brentford pushed for a precious winner, Clarke Oduor tapped in at the other end in the 91st minute.
BRAVE BARNSLEY, WIGAN WOE
There were contrasting scenes at full-time in the final regular league match at Griffin Park after Barnsley celebrated as Brentford collapsed.
The visitors were heading down until Oduor struck but stayed up at Charlton's expense, the Addicks going down 4-0 at champions Leeds United.
Wigan needed to win due to their deduction following administration, but one of the form teams in the division let a lead slip against Fulham, their total of 59 points bumped down to 47 to fall a painful point short.
SWANS SAVOUR GOAL SWING
Improbably, the Swans stole sixth place from Forest after a remarkable finale.
The Welsh side won 4-1, netting their fourth in the 91st minute as Wayne Routledge headed in his second.
That scoreline left Forest – 3-1 down at home to Stoke at the time – needing to score, but instead they conceded, their promotion bid derailing in spectacular fashion as Nuno da Costa stabbed into his own net in the sixth minute of stoppage time.
The 4-1 defeat meant Forest – without a win since July 1 – finished seventh.