In 1988, Moscow played the young Josh Baskin in Big, in which his character was magically transformed into an adult played by Tom Hanks. Moscow landed the role of David Jacobs in the 1992 filmed version of the musical Newsies, co-starring opposite Christian Bale. Moscow also appears in a leading role opposite Jessica Alba in the film Honey and has starred on several network television series including Zoe, Duncan, Jack & Jane. He was also featured on the television series Seinfeld as the character Lomez Jr in the episode "The Van Buren Boys". He’s also appeared in leading roles on Broadway, including Artie in the production What’s Wrong with This Picture at the Brooks Atkinson Theatre. Moscow ran A Theater Co. in New York alongside actors Tom Everett Scott from That Thing You Do! and Michael Kelly from House of Cards.

Moscow was born in The Bronx, New York City, the son of Patricia (née Sterner) and Jon Moscow. His mother's family is from Montana. His father is Jewish, and his mother is Mormon, but he was not raised in either religion. His younger brother Lev was an extra in Newsies and is a history Teacher at The Beacon School in New York City. David is friends with Max Casella and Luke Edwards from Newsies. Moscow attended Hampshire College in Amherst, Massachusetts, in the 1990s. He was engaged to Actress Kerry Washington from October 2004 to March 2007. David has been married to Karen Riotoc since September 2014.

Moscow has a long history as an Activist, which began in 1992 after dropping out of college to track wolves for the Round River Conservations Studies. He also built a mixed income green housing facility in Harlem in 2006. In 2007, the magazine Time Out New York reported Moscow's involvement in developing sustainable and economic housing in Harlem. He was active in the Bernie Sanders campaign, where he produced several PSA’s in 2016.

Moscow also co-developed and co-produced Lin-Manuel Miranda's first production of In the Heights with his ex-fiance, Actress Kerry Washington. As a Producer, his 2012 project, Hellbenders, was acquired by Lionsgate for North American and foreign distribution; and his film, the psychological thriller Desolation, David’s directorial debut, was partially funded by a successful Kickstarter campaign. Desolation has already been screened and honored at film festivals around the world including the Wroclaw Festival in Poland. Recent producing projects include Sylvio, The Jingoist, Blind, Easy Living and Thirst Street. He launched a Kickstarter to help fund post production with a video reenactment of the Zoltar "wish" scene from Big. The Kickstarter raised more than $70,000.