Killam was born on April 1, 1982 in Culver City, California, and grew up in Big Bear Lake, California. He graduated from the Los Angeles County High School for the Arts. His great-uncle was actor Robert Stack. Killam attended the University of California, Los Angeles for one year in 2000.
In 1994, Killam made his first film appearance as an adolescent in Naked Gun 33⅓: The Final Insult. Killam was also featured on Nickelodeon's The Amanda Show, a sketch-comedy vehicle for Amanda Bynes, on which he played Spaulding, a boy who had a huge crush on Moody, in the soap opera parody "Moody's Point."
Killam joined the cast of MADtv as a featured player during its seventh season from 2001 to 2002. Although, of the 25 episodes that aired during MADtv's seventh season, Killam only fully appeared in 13 episodes. Joining the MADtv cast at age 19, Killam was the youngest cast member ever hired on the show and the only cast member on MADtv to get his start on children's shows (similar to Kenan Thompson on Saturday Night Live). He was also a regular cast member on the third and fourth seasons of Nick Cannon's Wild 'N Out. In 2005, Killam co-starred in the television pilot Nobody's Watching, which never aired on network TV. The pilot, however, gained popularity after it was leaked online and they continued making webisodes from 2006 to 2007.
Killam co-starred in the 2004 Disney Channel Original Movie Stuck in the Suburbs. After MADtv, Killam appeared on TV shows such as Jake in Progress, Still Standing, Boston Public, Drake & Josh, Do Over, Roswell and Judging Amy. He had also appeared on Scrubs and Scrubs: Interns as Jimmy (the Overly Touchy Orderly). Killam appeared as a contestant on the episode of The Price Is Right which aired on December 7, 2006. The episode was re-aired on July 19, 2007.
He has also been in Big Fat Liar, Just Married, Anderson's Cross, and My Best Friend's Girl.
Killam was a member of the Los Angeles-based improvisational and sketch-comedy troupe the Groundlings. He retired from the main company in 2012.
On September 25, 2010, Killam joined the cast of Saturday Night Live for the 36th season, making him the second Nickelodeon veteran (after Kenan Thompson) to join SNL and the second SNL cast member who was previously a cast member on the sketch show MADtv (after Jeff Richards). Killam has named Eddie Murphy as his favorite SNL cast member and Arcade Fire as his favorite musical guest. On August 8, 2016, Killam was dropped from the cast.
|1994–2002||All That||Himself||15 episodes; also writer|
|2000||The Jersey||Varsity 1||Episode: "Nick's a Chick"|
|2000||Judging Amy||Freddie Felleman||Episode: "The Wee Hours"|
|2000||Touched by an Angel||Teenage Robert||Episode: "The Grudge"|
|2000–2002||The Amanda Show||Spaulding prof||7 episodes|
|2001||Roswell||Malamud||Episode: "Heart of Mine"|
|2002||Do Over||Dave||Episode: "The Block Party"|
|2004||Drake & Josh||Trevor||Episode: "Dune Buggy"|
|2004||Boston Public||Alex Buchanan||Episode: "Chapter Seventy-Eight"|
|2004||Still Standing||Andy, Varsity Basketball Player #1||Episode: "Still Narcing"|
|2004||Stuck in the Suburbs||Jordan Cahill||TV film|
|2005||Jake in Progress||Todd||Episode: "Loose Thread"|
|2006||Girlfriends||Jordan Gray||Episode: "Hustle & Dough"|
|2006–2014||How I Met Your Mother||Gary Blauman||6 episodes|
|2006–2007||Wild 'n Out||Various||29 episodes|
|2007||Nick Cannon Presents: Short Circuitz||Various||8 episodes; also writer|
|2009||Scrubs: Interns||Jimmy||Episode: "The Late Night with Jimmy Show"|
|2010–2016||Saturday Night Live||Himself, Various||Main role|
|2011||Community||Cory Radison||Episode: "Regional Holiday Music"|
|2012||iCarly||Agent Kinsey||Episode: "iMeet the First Lady"|
|2012||Saturday Night Live Weekend Update Thursday||Patient, Steve Doocy, Guy||2 episodes|
|2013–2015||Drunk History||William Clark, Frédéric Auguste Bartholdi, Bobby Fischer||3 episodes|
|2013–2015||The Awesomes||Zip "Frantic" Danger (voice)||Main role|
|2014||Comedy Bang! Bang!||Smith Calvins||Episode: "Jenna Fischer Wears a Floral Blouse & Black Heels"|
|2014||Sesame Street]'||Professor Buck Awe||Episode: "School for Chickens"|
|2015||Nature Cat||Nature Cat||Voice|
|2016||New Girl||Fred||Episode: "What About Fred"|