IGN's Eric Goldman says:
After a lot of back and forth -- going back many months -- about whether Jason Momoa (Game of Thrones) would play Aquaman in Batman v Superman: Dawn of Justice, it now looks like the actor will indeed be putting on the green and orange outfit of Arthur Curry.
Hitfix's Drew McWeeney is reporting the news, noting that while Warner Bros. haven't made the official announcement, Hitfix "can confirm that he will be playing the part, and that Zack Snyder has already finalized his designs for the character so shooting can take place soon."
Rumors about Momoa playing Aquaman began last year, but he'd downplayed or outright denied them previously. In fact, when IGN's Roth Cornet spoke to the actor in January, he said, "It's just rumors. I want to say something amazing, but I can't comment on rumors. It's flattering." Momoa than more definitively added, "I'm not involved in it." Indeed, Momoa has continued to deny he was playing [Aquaman](movie:264237) as recently as last month.
Perhaps at the time IGN spoke to him, Momoa was still in the negotiation stage, and no doubt he's been sworn to secrecy, even as things were solidified, but McWeeney -- who is a proven, trusted source -- now says his involvement is a done deal, and that it will, not shockingly, lead to a bigger role in the Justice League film.
Hitfix goes on to say they also know how Aquaman will be used in [Batman v. Superman: Dawn of Justice](movie:711870), noting it will piggyback off of the much-discussed (and debated) mass destruction that occurred in Man of Steel. Read on if you want to know the setup for Aquaman, per Hitfix:
Someone else who's not particularly happy about what happened in that film is Aquaman. I'm not sure if that's the actual name they'll use or not, but what we're hearing is that he is not pleased about the World Engine and what it did to the Indian Ocean. He will not have a major role in the film, but he will make an appearance, and it definitely sets him up to return once Snyder gets to "Justice League."