An average total of 28 million watched TV between 6pm and 10.30pm, BARB figures show.
BBC News Online said it was the biggest audience on record since 1992, when current research methods began. And that figure is likely to increase further once recorded viewing figures are added this week.
The record ratings included the 17.2 million that tuned in to see Matt Cardle crowned this year’s X Factor winner, as well as an average 11.6 million who watched Gavin Henson leave the Strictly competition.
Piers Morgan’s interview with Sir Elton John and a screening of Dirty Dancing also boosted figures.
At one point, between 8.45pm and 9pm, an average of 31.9 million people were watching a television programme.
David Bunker, head of research at BBC Vision said: “It’s remarkable to get that many people watching TV.
“It’s as much about all channels offering something for all audiences. Antiques Roadshow and The X Factor are at two ends of the spectrum – hence you get massive audiences”.
Peter Fincham, ITVs director of teleivsion, said: “An audience of 20 million is a phenomenal achievement for any channel in the modern digital age”.