He was nominated for the Tony Award for Best Featured Actor in a Play for his performance as Richard Miller in Ah, Wilderness!

Off-Broadway, he starred in Dealer's Choice, My Night with Reg, If Memory Serves, and Ancestral Voices, as well as in Kit Marlowe at the Joseph Papp Public Theater.

[2][3][4][5] Trammell's big break came when he landed the role of Sam Merlotte on the HBO series True Blood.

He played Hazel (Shailene Woodley)'s father, Michael Lancaster, in the 2014 film The Fault in Our Stars,[6] based on the novel of the same name by John Green.

[7] He played Vice-president Benjamin Hayes in the final season of Homeland who is signed in as Commander-in-chief after the sitting President is killed.