GAME of Thrones is now the most-watched series in Australian subscription television history.

Yesterday's premiere of the fifth season of the hit fantasy drama broke ratings records for Foxtel.

A combined cumulative average audience of 553,000 viewers tuned in to the first episode of season five yesterday, a 76 percent increase on last season according to the pay-TV provider.

That number is expected to grow as subscribers who missed yesterday's premiere catch up throughout the week.

Foxtel is the Australian broadcaster of Game of Thrones, which is locked in an exclusive deal for the life of the show which even excludes Foxtel's own streaming video on demand service Presto.

The first screening of episode one at 11am yesterday, which aired at the same time in 170 countries around the world, was seen by 242,000 Foxtel subscribers.

A further 311,000 tuned in to the encore screening at 7.30pm on the Showcase channel.

According to Nielsen Twitter TV ratings, Australians viewed more than half a million Game of Thrones related tweets last night, which would make the season five premiere the biggest non-sport TV event on Twitter in Australia.