Faustino was born in Los Angeles, California, on March 3, 1974, to Roger and Kay Faustino, a costumer. His older stepbrother Jeff Leiber is also an actor, and his younger brother Michael made many guest appearances on Married... with Children, including the episode David wrote, "T*R*A*S*H".

Faustino made his television debut at the age of three months when he appeared on the Lily Tomlin Special. He did not start regularly acting until 1980 after a smaller part on Little House on the Prairie. Throughout the early to mid-1980s, Faustino guest-starred on many well-known television series such as Family Ties, St. Elsewhere and The Love Boat. He also guest-starred in many not-so-well-known television series, but in 1987, he landed a full-time gig on Married... with Children

Fox's Married... with Children was Faustino's big break, as he played Bud, the younger of the two Bundy children. He played the character from its debut on April 5, 1987, until its final episode broadcast on June 9, 1997. Faustino appeared in 259 episodes. While filming the sitcom throughout the 1990s, Faustino continued to make guest appearances in many sitcoms and dramas. He reprised the role of Bud Bundy in such series as Parker Lewis Can't Lose and Top of the Heap. Faustino also appeared on Burke's Law, MADtv and The New Addams Family.

Faustino co-founded and co-hosted a night club in Los Angeles named Balistyx, which is the same name as his rap album. The club was "the first hip-hop/funk club on the Sunset Strip", and was originally held on Thursday nights at the Whisky a Go Go in 1991. The club closed after a final New Year’s Eve party at The Roxy to ring in 1993.

In 1992, D' Lil released the album Balistyx, which spawned one single entitled "I Told Ya".

In 2002, he appeared in the reality television special Celebrity Boot Camp (a shortened version of the Boot Camp series for celebrities). In 2001, he appeared in the low-budget film Killer Bud produced by Aglet Productions. In 2005, Faustino guest-starred on two episodes of One on One with one of the roles was as Flex Washington's agent.

After meeting at a spiritual center in Los Angeles and dating for five years, he married Andrea Elmer on January 24, 2004, at the Little White Wedding Chapel in Las Vegas, Nevada. They separated in May 2006. Faustino sought not to pay spousal support, according to the papers filed in Los Angeles. On February 6, 2007, Faustino officially filed for divorce in Los Angeles County Superior Court, citing irreconcilable differences.

Faustino was arrested for misdemeanor possession of marijuana in May 2007. A disorderly intoxication charge was later dropped after Faustino agreed to enroll in a drug rehabilitation facility.

He co-wrote a 2008 independent electronica album with Austin-based musician Jon Dishon titled Hollowdreams which he also produced alongside close friend Corin Nemec.

Faustino appeared with the cast of Married... with Children again at the 7th Annual TV Land Awards in 2009, presented by Dr. Phil. He also had cameo appearances in two episodes of the HBO series Entourage and co-starred in the feature Not Another B Movie which was distributed by Troma Entertainment in 2011.

By 2012, Faustino was cast in The Legend of Korra as the voice of firebender Mako, a central character named after the late Mako Iwamatsu (the voice of Iroh in the original series). He also played Dagur the Deranged as a secondary villain on season one and main villain in season two of DreamWorks Dragons. He appears in the Bones 12th-season episode "The Radioactive Panthers in the Party", playing a fictional version of himself as a suspect in the death of an aspiring filmmaker.

On November 14, 2015, his girlfriend Lindsay Bronson gave birth to their daughter, Ava Marie Grace Faustino.

"This is a very twisted take on what I’ve been through all these years," Faustino said. He has also signed a deal with National Lampoon to be involved with three low-budget films.