The third run of the HBO drama's adaptation of George RR Martin's Song of Ice and Fire series of novels will be based on the first part of the longest entry A Storm of Swords.
The showrunners explained that while the third season will still have 10 episodes, a whole extra episode's worth of material will be included.
"There's almost another full episode's worth of extra minutes spread across the season," Weiss told Entertainment Weekly.
"One of the great liberties with HBO is we're not forced to come in at a specific time. We can't be under 50 minutes or over 60, but that gives us a lot of flexibility."
"A super-sized season, as befitting Storm of Swords," Benioff added. "Last year we had a lot of 52-minute episodes. This year is a lot of 56, 57."
The third season finale episode is also expected to run for over an hour, following suit from the final episode of season two.
HBO said in a statement: "All 10 episodes gained a minute or two from past seasons with the finale very possibly exceeding 60 minutes."
"So for people clamouring for another episode, it's in there," Weiss added. "It's just been cut into tiny pieces."
Game of Thrones' third season premiere will air on March 31, 2013 on HBO. The show is broadcast on Sky Atlantic in the UK.