Ronson scored a global hit with the 2014 track, which features Mars on vocals, and the song topped the charts in more than 20 countries including the U.S., where it spent a record 14 weeks at the top of the Billboard rundown.
Now the producer has opened up about the creation of the song, revealing Mars was instrumental in marshalling the musicians in the studio and acting as a sounding board for Ronson as the track developed.
He tells British magazine ST, "Bruno (is) such a perfectionist. And so - in a good way - hard on everyone around him to ensure everyone's delivering the best possible s**t. And that's why Uptown Funk sounds like it does...
"The song wouldn't have been as good if not for Bruno. I think people think I made Uptown Funk and sent it to Bruno to do the vocal. But that song is very much his creation. I remember spending three days in Memphis slaving over that song and thinking that we finally had it. I then got a call from him two days later saying, 'No, it's not it.' And I knew deep down it wasn't it either."
Mars is not the only star Ronson has credited over Uptown Funk - he has since added several musicians to the writing credits to avoid any copyright dispute, including members of The Gap Band for the track's similarity to their 1979 smash Oops Up Side Your Head.