Flores was born in San Diego, and raised in La Colonia Eden Gardens, a Mexican founded neighborhood in Solana Beach, California.
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 shortened to "Oh, What a Night". In 1994, his chin was shattered when he was shot in the jaw and in the eye later.
During his career, Lil Rob has collaborated with fellow Chicano rappers Mr. Shadow, Mr. Sancho, and OG Spanish Fly, and mainstream artists such as Paul Wall, The Game, E-40 and Pitbull. Lil Rob and Mr. Shadow were in a group called The Mayhem Click. The numbers twelve and eighteen, which are tattooed on his forearms, represent the numeric value of the letters L and R, the initials of his stage name. The number was used during his days as a graffiti tagger.
In 2002, Lil Rob left Low Profile Records and signed to Upstairs Records. He found commercial success with the 2005 release Twelve Eighteen (Part I) in which the single "Summer Nights" received national airplay, a first in his career. "Summer Nights" peaked at #36 on the Billboard Hot 100 and #13 on the Hot Rap Tracks chart. The follow-up single, "Bring Out the Freak in You", peaked at #85 on the Hot 100 Charts, and at #20 on the Hot Rap Tracks. The exposure led to small roles in the 2005 Cuba Gooding, Jr. film Dirty and the 2007 Rob Schneider vehicle Big Stan, both of which were released straight to DVD in the U.S.
On June 29, 2007, Lil Rob made his very first appearance overseas in Okinawa, Japan. 1218 (Part II) was released in 2008 and featured the single "Let Me Come Back" featuring Fingazz. In 2009, Love & Hate, was released, and in 2013, he released a new song called "Don't Want to Fall in Love".
In 2014, his ninth album, R.I.P. (Recording In Progress), was released.
Lil Rob was in conflict with Mr. Shadow, Royal T (CEO of Low Profile Records), and Mister D (CEO of Southland Records). Mr. Shadow would malign Lil Rob on hit singles, "Shadow of Your Death", "Excited" and "Excited 2". These songs were from the album Till I Die. One of the reasons why Mr. Shadow had problems with Lil Rob was because Mr. Shadow claimed that Lil Rob was not from San Diego. Mr. Shadow claimed that he was from Solana Beach. Mr. Shadow felt that Lil Rob was lying to everyone about being raised in San Diego, CA. In 2005, on the Twelve Eighteen (Part I) album, Lil Rob would speak ill towards Mr. Shadow, on the song "I Who Have Nothing".
Lil Rob feuded with Royal T, and eventually left his label, on account of marketing issues. Royal T, the executive producer of Low Profile Records, had created a scam that involved Lil Rob's albums to have the same bar code as Royal T's CDs, which resulted in Royal T automatically receiving the profits. According to Lil Rob's manager, Lil Rob sold over $1 million worth of his own CDs and didn't receive a dime. As soon as Lil Rob left Low Profile, Lil Rob recorded a diss aimed towards Low Profile, entitled "The Last Laff" on The Last Laff EP. Low Profile Records responded with a track entitled "Riders", featuring Royal T, Payaso (Dukes Click), Lil' Bandit & Mr. Sancho. Lil Rob recorded another diss track entitled "Call the Cops", directed at Royal T on 2002's The Album. Lil Rob also recorded diss tracks "Bluffin'", dissing directly at Royal T and "Boo Hoo Hoo" dissing both Royal T and Mr. Shadow off of 2004's Neighborhood Music.
Lil Rob has collaborated with musicians such as Mr. Shadow, Lil Cuete, Royal T, Mr. Lil One, Mr. Sancho, OG Spanish Fly, Silencer, Fingazz, Kid Frost, Frankie J, J. Cole, Ludacris, Pitbull, N.O.R.E, Chingo Bling, Bizzy Bone, Far East Movement, Baby Bash, The Game, Ice Cube, WC, Dyablo, NB Ridaz, SPM, Fat Joe, Paul Wall, Flo Rida, Voltio and C-Kan.