It received record ratings in the US, with a total audience of 11.7 million across all platforms.
The show has also become the most pirated television series in the world. According to website Torrentfreak, the final episode of the second series in 2012 was illegally downloaded by some 4.3 million people.
"I probably shouldn't be saying this, but it is a compliment of sorts," HBO director of programming Michael Lombardo said in a recent interview.
"The demand is there. And it certainly didn't negatively impact the DVD sales. (Piracy is) something that comes along with having a wildly successful show on a subscription network."
HBO's decision to approve a fourth season of the show was considered a formality, with the third season covering only half of A Storm of Swords, the acclaimed third book of Martin's series.
The next season is expected to cover the second half of the book.
Game of Thrones is a particularly expensive show to make, with elaborate sets scattered through Ireland, Croatia and Iceland.
- nzherald.co.nz