James Arthur's triumph in Sunday's climax peaked with 12.5m - a 44% share - when the result was announced.
Meanwhile, an average of 10.94m (39.1%) watched ITV1's two-hour broadcast between 7.40pm and 9.40pm, adding 133,000 on +1.. The figure represents 15% drop on Little Mix's victory last year, and over 30% down on the show's peak year of 2010 when Matt Cardle won.
However, the finale rated better than expected when considering that this year's series launched with an average of 8.1m. The Xtra Factor followed the main show on ITV2 with 1.61m (7.6%) and 116k an hour later on +1.
Strictly Come Dancing's results programme, which aired at the earlier time of 7pm, rallied to 9.95m (37.7%) on BBC One and was the night's second most-watched broadcast, while Antiques Roadshow (5.82m/20.9%) held up remarkably well against the first hour of X Factor.
Elsewhere on the channel, Countryfile pulled in 6.66m (28.6%) earlier on at 6pm, and documentary Rome's Lost Empire interested 3.93m (14.3%) from 8.40pm.
After X Factor finished, viewers deserted ITV as Rod Stewart's Christmas posted an audience of just 3.5m (16.3%) in the network's lucrative slot as well as 130k on timeshift. Celebrity Who Wants to be a Millionaire? preceded the Simon Cowell singing contest with 2.83m (11.1%) from 6.40pm (+1: 130k).
Channel 4's best audience of the day came at 5.15pm for its screening of Elf, which grabbed an impressive 3.5m (15.4%) and 654k on +1. The broadcaster posted audiences of 2m (7.4%) for Homeland at 9pm (+1: 352k) and 845k (3.9%) for Peep Show at 10pm (+1: 160k).
A film also topped Channel 5's night as The Expendables took 2.02m (8.6%) between 9pm and 11.15pm, appealing to a further 281k on +1. And BBC Two's snooker coverage pocketed 1.25m (6.1%) from 8pm.
Overall, ITV1 predictably reigned over BBC One in primetime with 28.2% (+1: 0.5%) against 21%. 5 edged into third place with 5.8% (+1: 0.4%), pipping Channel 4's 5.6% (+1: 1.6%), and Channel 5's 5.8% (+1: 0.4%).
BARB ratings data supplied by Attentional