The David Attenborough-fronted series saw its first episode received 4.2 million requests on the streaming service of the UK’s pubcaster.
This narrowly topped episode one of Tom Hardy drama Taboo, which took 4.1 million.
Relationship drama Doctor Foster’s second season opening was third with 3.7 million, and underage sex scandal drama Three Girls was fourth with 3.3 million requests for its opening episode.
The news will go down well with factual producers and commissioners, who have been largely in the shade throughout 2017 due to the widespread impact of new original dramas internationally.
With the news, the BBC is planning to keep Blue Planet II available until the New Year, and has released a special ultra-HD version, plus the original Blue Planet and both Planet Earth series.
Taboo is being re-released on the iPlayer on December 16, along with a number of other drama, comedy, natural history and kids shows. These include Three Girls, Sherlock and all four seasons of Line of Duty.
“It’s been an extraordinary record breaking year for BBC iPlayer with the awe-inspiring Blue Planet II coming out on top, closely followed by an incredible range of original drama as huge numbers have chosen Taboo, Doctor Foster, Three Girls, Sherlock, Apple Tree Yard and Line of Duty,” said BBC director of content Charlotte Moore.