ITV drama Victoria bowed out with 4.8 million viewers - its best overnight figures since the launch episode.
The lavish production, starring Jenna Coleman and Tom Hughes, is returning for a second series next year.
Sunday night's final episode was watched by 5.5 million people and took a 25% share of the audience. The number of viewers peaked at six million.
It was the highest overnight rating since the launch episode, when the big-budget drama attracted 5.7 million viewers and 6.1 million at its peak.
Poldark, on BBC1, which was also broadcast at 9pm, was watched by 4.9 million viewers and took a 22% audience share.
ITV's figures include catch-up on its plus one channel.
On BBC1, Strictly Come Dancing's results show - broadcast from 7.15pm to 8pm - had a peak audience of 9.7 million, and averaged nine million with a 41.1% audience share, making it the best results for a Sunday this series so far.
The X Factor, which went out at 8pm on ITV, was seen by 6.5 million viewers and a 28% share, with a peak of 7.5 million viewers, making it the broadcaster's most watched programme of the night.