Flores grew up in La Colonia de Eden Gardens, a Hispanic-American enclave in Solana Beach, California. He was a fan of 80s funk bands like the Gap Band and the S.O.S. Band.
In the early 1990s, he began performing under the name Lil Rob & the Brown Crowd, and recorded a single titled “Oh, What a Night in the 619”. Though it did not chart, it was later featured on his 1997 debut album Crazy Life, with the title trimmed to “Oh, What a Night”. Lil Rob has worked with fellow Chicano rappers Mr. Shadow, Mr. Sancho, and OG Spanish Fly, as well as mainstream artists Paul Wall, The Game, E-40, and Pitbull. Mr. Shadow and Lil Rob were members of The Mayhem Click. The tattooed digits twelve and eighteen symbolize the numeric value of the letters L and R, the initials of his stage name.
Lil Rob left Low Profile Records in 2002 and signed with Upstairs Records. In the 2005 release Twelve Eighteen (Part I), he experienced commercial success, as the single “Summer Nights” garnered national airplay, a first in his career. “Summer Nights” reached number 36 on the Billboard Hot 100 and number 13 on the Hot Rap Songs chart. “Bring Out the Freak in You,” the follow-up single, peaked at #85 on the Top 100 Charts and #20 on the Hot Rap Tracks. The publicity led to brief roles in the 2005 Cuba Gooding, Jr. picture Dirty and the 2007 Rob Schneider film Big Stan, both of which were released on DVD in the United States.