The Stephen King adaptation has the biggest audience for a first-year drama at the premium cable outlet since 'Westworld.'

HBO's The Outsider has quietly racked up a big audience over the course of its 10-episode run.

The adaptation of Stephen King's novel hasn't received the media attention of, say, Watchmen or Big Little Lies — but it's brought in more viewers than the former and is approaching the latter's mark in multiplatform audience. The Outsider is drawing the biggest audience for a first-year HBO drama since Westworld in 2016.

Through its first nine episodes, The Outsider — which stars Ben Mendelsohn and Cynthia Erivo as a detective and private investigator looking into the mysterious circumstances surrounding a boy's death — has averaged better than 9 million viewers per episode across all platforms. (HBO's viewer figures are for the entire run of the show to date.)

Sunday's finale drew the biggest initial audience for the show with 1.37 million people tuning in. That's a 16 percent improvement on the previous high of 1.18 million set a week earlier. Replays and streaming pushed Sunday's total to 2.2 million, a first-night high for the show.

The all-in audience figures for The Outsider are ahead of both the fall run of Watchmen (7 million viewers over a similar amount of time) and the third season of True Detective (8 million), which ran in January and February 2019 — and like The Outsider, aired episodes opposite the Super Bowl, the Grammy Awards and the Oscars.

Season two of Big Little Lies, meanwhile, averaged 10 million multiplatform viewers during its summer 2019 run.

The Outsider has drawn smaller initial audiences than did True Detective, averaging about 915,000 viewers for its on-air debut versus 1.25 million for True Detective. Replays, delayed viewing and streaming have more than made up the difference.

The Outsider is produced by Media Rights Capital, which shares a parent company, Valence Media, with The Hollywood Reporter.