The star revealed he was finished with the franchise when he appeared on the SmartLess podcast on Monday (31 August).
Podcast host and actor Jason Bateman asked, “I’m assuming that the Marvel thing is at a slower speed now, or are you done with that now?”
The 55-year-old was brief and clear in his reply, stating: “That’s all done.”
The news will come as a disappointment to fans who were hoping for an Iron Man return.
Rumours were circulating that the actor might reprise his role in some capacity in the forthcoming Black Widow film.
In an interview in January, Downey Jr told Extra TV that “anything could happen,” but went on to add: “As far as I’m concerned, I hung up my guns and I’m good to let it go.
“ I also think that Marvel is on this journey now, they’re trying a bunch of other stuff and you know, I’m excited for them to see how all that goes,” he said.