Kellum is best known for his roles as Curtis Holt on The CW drama series Arrow, Tommy on the Fox sitcom Ben and Kate,[4] Hunter on NBC's Sean Saves the World,[5] and Noah Koles on NBC's Grand Crew.

[6] Born in Chicago, Illinois,[7] he moved to Los Angeles in late 2009 to pursue a career in comedy.

In 2015, Kellum was cast in the recurring role of Curtis Holt, based on the DC Comics character Mister Terrific, in the fourth season of The CW drama series Arrow.

[14] In 2017,[15] Kellum appeared in Netflix's Girlfriend's Day[16] as Madsen, beat poet and a co-worker of Bob Odenkirk's character.

[17] Kellum voices the character "King Joaquín" on the Disney Channel animated series Elena of Avalor.