The Captain America: Civil War star took to Facebook on Friday to congratulate his son Indio, 22, on his sobriety and new music.
"Congrats are in order for my firstborn, and I'm proud to oblige," the actor, 50, said of his son with actress/singer Deborah Falconer.
"Having braved the crucible of addiction (and pleased the court), his ongoing commitment to recovery continues to inspire and amaze," he continued.
Earlier in the month, Indio's felony cocaine possession conviction was dismissed after he successfully completed a 20-month rehab program.
"Unfortunately there's a genetic component to addiction and Indio has likely inherited it," Downey Jr. told PEOPLE of his son's arrest. "Also, there is a lot of family support and understanding, and we're all determined to rally behind him and help him become the man he's capable of being."
VIDEO: Robert Downey Jr. Teams Up With Make-A-Wish to Make a Little Boy's Wish Come True
In his Facebook post, the actor went on to gush over his son's musical accomplishments. "As long as we can remember, Indio has been a musician at heart. In the last several years, with his band mate Ralph Alexander, I've witnessed their dedication, consistency, and determination to grow as artists.
"I've also made it my business to be of as little help as possible, as nepotism usually does more harm than good... Just for today, I'm gonna ease up on that. Trust me and give these fine young men a listen," he concluded, while providing links to Indio's music.
His son's band, The Dose, recently released a new song, "Cold Hands" to iTunes.
Meanwhile, Downey Jr.'s latest turn as Iron Man in Captain America: Civil War opens May 6.