LaMonica Garrett was born in San Francisco, California. He was named after former Oakland Raiders quarterback Daryle Lamonica, of whom his parents were fans.

After high school, he attended a Los Angeles junior college where he played as a linebacker. Eventually, Garrett transferred to Central State University in Ohio where he continued to play. At one point, he led the team in tackles. Garrett considered joining the NFL, but despite having what he called "a great Pro Day" and having some workouts with the Detroit Lions and the Los Angeles Rams, he wasn't picked up.

While still a Slamball player, Garrett landed a role on an episode of One Tree Hill that had a Slamball-related storyline. After that, he signed with an agent and continued to get minor roles in TV shows like Hawthorne, CSI: Miami, and NCIS, as well as films like Transformers: Dark of the Moon. In 2011, Garrett started a recurring role as Deputy Sheriff Cane on FX's Sons of Anarchy. He appeared in 17 episodes from 2011 to 2014.

In 2016, Garrett landed two key roles; the first one, as Lieutenant TAO Cameron Burke on TNT's The Last Ship, and the second as Secret Service agent Mike Ritter on ABC's Designated Survivor. David Guggenheim, creator and executive producer of the latter, said they "needed someone who could throw Jack Bauer into a car", but that had "an emotional core goodness". The character of Mike Ritter became a fan favorite and Garrett remained with the show through the whole first two seasons, until its initial cancelation.

He was cast as Mar Novu / The Monitor in the Arrowverse crossover event "Elseworlds" on The CW, which connects storylines from The Flash, Arrow and Supergirl.

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