He is notable for playing the roles of Tactical Officer Lieutenant Felix Gaeta on the Sci-Fi Channel television program Battlestar Galactica, Emil Hamilton in Smallville, Jacapo Sinclair on The CW series The 100, and Dr. Cerberus on the Netflix series Chilling Adventures of Sabrina.

Juliani provided the voice of Toa Vakama of the Bionicle and later of Aaron Fox on Nexo Knights.

[citation needed] He was the voice of Pit/Kid Icarus in the Captain N: The Game Master cartoon series, and offered his voice in many other cartoons and anime including the English version of Death Note's L, Ranma ½ (as Toma), X-Men: Evolution (as Gambit), the three My Scene films (in the role of River) and two of the Bionicle films (as Toa Vakama).

In 2002, he played a grieving Chinese opera performer in Ann Marie Fleming's short film Blue Skies.

In 2003, the 1978 television series, Battlestar Galactica was brought back to the small screen in what was termed a "reimagined" form, as a three-hour miniseries.

In March 2009, Juliani won the Streamy Award for Best Male Actor in a Dramatic Web Series for his work in the webisode, Battlestar Galactica: The Face of the Enemy.

Juliani has performed the narration for audio books, including METAtropolis and in 2011 Stanislaw Lem's Solaris: The Definitive Edition.

[10] From 2014 to 2017, Juliani had a recurring role as Sinclair, a member of the Ark crew on The CW science fiction series The 100.