Kelley's first major acting role was in the 2002 film Antwone Fisher, in which he played the title character as a child.

Prior to this, he appeared in several small television roles in programs such as Malcolm in the Middle and Judging Amy.

[1] A regular cast member in the show's first season (2004–2005), he appeared only occasionally thereafter due to a dramatic growth spurt.

He reprised the role of Walt a final time in the Season 6 DVD box set mini-episode "The New Man in Charge".

Following his departure from the main cast of Lost, Kelley appeared in several television roles, including the recurring character of Benjamin Cooley on Saving Grace.