The actor will be playing the superhero again in the third film, following Jon Favreau's departure as director.
He told Hero Complex: "Bringing in Shane Black to write and direct Iron Man 3 to me is basically the only transition from Favreau to a 'next thing' that Favreau and the audience and Marvel and I could ever actually sign off on."
Downey Jr and Black previously collaborated on 2005's Kiss Kiss Bang Bang.
"[Black's] more than the sum of his parts and he's also kind of been a sleeper for a long time," Downey Jr continued.
"We're not talking much about [the script] right now because Shane is off writing and we talked before that, and when we are talking again the talking is going to be over pretty quick [because we're on the same page]."
Downey Jr will next be seen in the titular role in Guy Ritchie's upcoming Sherlock Holmes: A Game of Shadows.
Watch the trailer for Iron Man 2 below: