Julie Walters played Mo Mowlam in the film
Channel 4's biopic of Mo Mowlam was the highest rated drama for the station for more than eight years, according to overnight ratings.
The film, starring Julie Walters, drew an average of 3.5 million viewers when it was screened at 2100 GMT on Sunday.
The story of the former Northern Ireland Secretary's battle with cancer and her efforts to unite NI's leaders had a peak audience of 3.7 million.
A spokeswoman said it was Channel 4's highest rating drama since 2001.
Audience figures also showed that C4's final series of Celebrity Big Brother went out on a high, beating last year's finale shows.
The second of Friday night's programmes, in which cage fighter Alex Reid was named the winner of the series, had an average of 4.1 million, with a quarter of TV viewers tuning in.
Last year the equivalent show drew just 3.5 million.