Sheffield United confirmed their return to the Championship after a six-year absence with victory at Northampton.
The Blades knew a win was enough to send them up and, after Marc Richards put the hosts ahead, Leon Clarke and John Fleck scored to secure promotion.
Chris Wilder made a triumphant return to Northampton, having led the Cobblers to the League Two title last season.
United will win the League One title if they take four points from their final four games of the campaign.
Even if the Blades had lost, they would still have been promoted as third-placed Fleetwood were beaten at Oldham.
Blades end long wait to leave League One
Promotion from League One has been a long time coming for United, who were relegated from the Championship under Micky Adams in May 2011.
They had three failed play-off campaigns in their previous five seasons in the third tier, but have secured automatic promotion this time around with four games to spare.
Danny Wilson, David Weir, Nigel Clough and Nigel Adkins all had spells in charge of the Blades before Wilder, a boyhood Sheffield United fan, was named as manager in May 2016.
Wilder’s appointment came shortly after he had led Northampton to automatic promotion from the fourth tier, but he made a slow start as his new side took only one point from his first four league matches.
However, the Blades have lost only three more league games since 20 August and have not dropped outside the top two places in the division in 2017.
Key to the club’s success this term has been captain and striker Billy Sharp, who has scored 26 goals in 42 league outings this season.
Since the start of the 2015-16 season, Wilder has taken charge of 88 league matches and won 55, collecting 187 points.