[1] He rose to prominence for playing Leslie Chow in The Hangover film series (2009–2013) and Ben Chang in the NBC sitcom Community (2009–2015).

He created, wrote and produced the ABC sitcom Dr. Ken (2015–2017), in which he portrays the titular character, and he has appeared in the films Knocked Up (2007), Role Models (2008), Furry Vengeance (2010), The Duff (2015), Ride Along 2 (2016), Crazy Rich Asians (2018), Scoob!

He was a regular at open mic nights in the Raleigh-Durham circuit, performing at Charlie Goodnights in Raleigh and Tootie's Durham Comedy Club.

He also emceed The Comedy Spot programming series on Duke University campus 1992 and 1993 (produced by his friend Kendrick Jahng) opening for Margaret Cho, Jeff Dunham, and others.

NBC president Brandon Tartikoff and The Improv founder Budd Friedman were judges and they both urged Jeong to move to Los Angeles.

His stand-up work led to several television appearances, including NBC's The Office, FOX's MADtv, HBO's Entourage, and Curb Your Enthusiasm.

[3][9] Early in Jeong's career, he studied with director Natalia Lazarus at the Los Angeles Performing Arts Conservatory where she coached him for his film debut in Knocked Up.

Jeong played Señor Chang on the NBC sitcom Community and was nominated for the show's "Male Breakout Star" at the 2010 Teen Choice Awards.

On May 22, 2011, he hosted the 2011 Billboard Music Awards in Las Vegas on ABC[14] and was featured in a Hands Only CPR PSA campaign from the American Heart Association on June 15, 2011.

In 2015, Jeong starred, wrote, and executive produced the pilot of his new ABC medical comedy, Dr. Ken, as a frustrated HMO doctor juggling his career, marriage, and parenting, but succeeding at none of them.

On May 7, 2015, the series was ordered by ABC to debut in the 2015–16 TV season starring Jeong, Suzy Nakamura, Dave Foley, Tisha Campbell, and Jonathan Slavin.

In January 2019, Jeong made a guest appearance on King of Mask Singer, performing "Creep" by Radiohead as the Golden Pig.

"[30] In February 2020, Fox named Jeong as host and co-executive producer of its upcoming music game show I Can See Your Voice, also based on a South Korean format.

[44] Jeong and his close friend and Community costar Joel McHale[45] have hosted a podcast together titled The Darkest Timeline.