With just four wins in the Sky Bet Championship all season, the writing has been on the wall for a long time, but Sone Aluko's second-half goal was enough to confirm the Millers' return to League One.
It was a 30th defeat of a miserable campaign and, with six games left, Rotherham could break the Football League record of 34 for the most losses in a season.
The three points did wonders for Fulham's hopes of leaving the division at the other end as they moved into the play-off positions and their top-six aspirations are now in their own hands.
They were boosted just before kick-off by news from 15 miles up the M1 that Sheffield Wednesday had only drawn at Barnsley, so they knew a win would send them above the Owls.
Wednesday led at Oakwell through Sam Winnall's goal early in the second half but Angus MacDonald headed an injury-time equaliser for the Tykes
Newcastle and Brighton each took another step towards automatic promotion after they won and Huddersfield lost at home
Leaders Newcastle remain a point clear at the top after beating relegation-threatened Wigan 2-1 at St James' Park
Dwight Gayle's 22nd goal of the season gave the Magpies the half-time lead but Michael Jacobs equalised five minutes into the second half
However, Wigan were level for just seven minutes as Matt Ritchie restored Newcastle's lead.
Glenn Murray's 67th-minute strike saw Brighton beat Blackburn 1-0 at the Amex Stadium to inflict a first defeat on Rovers boss Tony Mowbray, whose side stay in the bottom three.
Huddersfield are now nine points behind Brighton after they lost 1-0 at home to Burton, with Jackson Irvine's effort deep into injury time moving Nigel Clough's team four points clear of the relegation places
Dean Whitehead was sent off for the hosts after 88 minutes.
Bristol City remain one point above the drop zone after losing 2-0 at Brentford
First-half goals from Sergi Canos and Lasse Vibe gave the Bees the three points
Nottingham Forest moved a point further away from danger after a 1-1 draw with Preston
Britt Assombalonga gave the Reds the half-time lead at Deepdale but Aiden McGeady equalised early in the second half
Ipswich and Birmingham are both six points above the bottom three after sharing a 1-1 draw at Portman Road
Jonathan Grounds gave Birmingham the lead but Grant Ward levelled things up for the hosts
Wolves won at home against Cardiff
A Danny Batth double and a goal from Helder Costa gave them a 3-1 victory, with Kenneth Zohore replying
Aston Villa continued to finish the season strongly after Jonathan Kodjia scored both goals in a 2-0 home win against Norwich, who had Ivo Pinto sent off with 10 minutes left
Source : PA