Romeo

He soon released his debut single "My Baby" in 2001 which peaked at number 3 on the Billboard Hot 100. Later the same year, Miller released his debut album Lil' Romeo, which charted the US Billboard 200 at number six selling 99,000 copies in its first week and went on to be certified Gold.

In 2001, Miller began his acting career with a cameo appearance in the Walt Disney Pictures' film Max Keeble's Big Move. In 2002, Nickelodeon offered him his own show, Romeo!, which ran for three seasons.  In 2003, he co-starred with Jessica Alba, Mekhi Phifer and Zachary Isaiah Williams in the dance film Honey. Also in 2003, he voiced himself on an episode of the animated series, Static Shock, to which he had performed the theme song.

He starred in another film with Zachary Isaiah Williams, God's Gift, which was released in 2006. He went on to co-star with his father in a film called Uncle P in 2007. His next project in 2007, was a film called ASL in which he starred as himself, alongside Forrest Lipton and Zachary Isaiah Williams who played the young Romeo; Williams had previously co-starred with Romeo in two films and Nickelodeon's Romeo!. He also made a cameo appearance in Ned's Declassified School Survival Guide as a rapping coach.

In 2007, Miller was offered and accepted a scholarship to play basketball for the USC Trojans at the University of Southern California. He played for the team until he was let go before his junior season in 2010. On July 24, 2010, Romeo launched his own clothing line titled "College Boyys".

He guest-starred as a rapper accused of murder in the 2010 CBS series The Defenders. In 2011, he also starred in TV commercials for McDonald's and ICDC College. He starred in the feature films Jumping the Broom (2011) and Tyler Perry's Madea's Witness Protection (2012). Also in 2012, he participated in Fox's dating game show The Choice.

On November 13, 2013, he revealed that he was working on a brand new clothing line titled ROME Everything. He was cast in the 2017 feature film Never Heard, also starring his father, Master P. In 2020, he and his father appeared on the reality series Celebrity Watch Party. In February 2022, it was announced he had landed a role in the Lifetime movie, Wrath: A Seven Deadly Sins Story, which aired on April 16.

He founded the record labels Guttar Music, Take a Stand, The Next Generation and his current label No Limit Forever Records.