As a teenager, Schwartz attended Stagedoor Manor Performing Arts Training Center in New York.
He began his career as a member of the comedy group The State and was featured on the television show by the same name on MTV. He continued working with members of that group on the show Viva Variety in the role of "Johnny Bluejeans", and in the film Wet Hot American Summer. His dry, sarcastically irreverent commentary on pop culture artifacts on VH1's "I Love the 70s/80s/90s/New Millennium" series has added to his and the shows' popularity. Black has stated several times on the show that he feels as if he is "doomed to an eternity of doing the 'I Love the...' series". He also makes fun of himself for being a Jewish-American and sarcastically enforcing the Jewish stereotypes.
In the latter part of 2004, he acted as guest-host of CBS's The Late Late Show while auditioning for the permanent hosting role. He was a finalist for the position, although the job eventually went to Craig Ferguson. He is also an occasional contributor to the online edition of McSweeney's, where he writes a column entitled "Michael Ian Black Is a Very Famous Celebrity".
Black, along with fellow State-rs Michael Showalter and David Wain, co-starred in and co-wrote the Comedy Central series Stella, a television adaptation of their popular stage show. The ten-episode first season debuted in June 2005 and was not renewed for a second season.
Black wrote the screenplays for two feature film comedies —Wedding Daze (The Pleasure of Your Company and The Next Girl I See, 2006) and Run, Fat Boy, Run (2007, co-written with leading actor Simon Pegg). Black also directed Wedding Daze which stars Jason Biggs, Joe Pantoliano, and Isla Fisher. Black also has some minor screen credits. He appeared twice on the Adult Swim show, Tom Goes to the Mayor, and was a guest voice on Seth Green's stop-motion show Robot Chicken. He appeared on the Comedy Central shows Crank Yankers and Reno 911!. He had a cameo in David Wain's 2007 film, The Ten as a prison guard. In September 2007, he released his first stand-up comedy album, I Am a Wonderful Man. Black also maintains a humorous blog at michaelianblack.typepad.com. In addition, he starred on the TV series Reaper (2008) as a gay demon trying to destroy the devil through acts of kindness. Most recently, Black wrote a book titled My Custom Van ... And 50 Other Mind-Blowing Essays That Will Blow Your Mind All Over Your Face, which was published on July 15, 2008.
Black is the host of Reality Bites Back, a scripted reality show that premiered July 17 on Comedy Central.
Black also developed another show for Comedy Central; Michael Ian Black Doesn't Understand. Which later retooled to a pilot which featured Michael Showalter called Michael and Michael Have Issues.
After being absent for several years, Black returned to the show in 2006, appearing in the second episode of the eighth season and playing for MAZON again. There, Black defeated Greg Behrendt, Jorge Garcia, Kim Coles, and Andrea Martin, and made Celebrity Poker Showdown history by knocking out three players (Martin, Coles and Garcia) in three consecutive hands. In the final table, he came in third (receiving $100,000 for his charity), with Jason Alexander winning the tournament (receiving $500,000 for his).
Black has made a mark in his appearances both for his jokes and antics and for his skilled, aggressive-but-controlled poker play. Black has been repeatedly praised by Dave Foley, host of Celebrity Poker Showdown, and by the two poker experts who have commented on the show, Phil Gordon and Phil Hellmuth. Gordon has listed Black among eight of the best celebrities he's ever seen on the show, and Hellmuth considered him one of the best players in the eighth tournament and a favorite to win after Jennifer Tilly's elimination. He and Foley argued over who would get to pick him to win in his two appearances.