Lenk was born in Camarillo, California, the son of Pam, a teacher, and Fred Lenk, a tuba player, high school music teacher, and school district computer network administrator. He attended Adolfo Camarillo High School. He graduated from UCLA with a Bachelor of Arts.
Lenk has appeared in episodes of Buffy the Vampire Slayer (27 episodes), Angel, NBC's Joey, House, Six Feet Under, Eli Stone and How I Met Your Mother. He has also had small parts in the films Date Movie, The Number 23, and Transformers. Lenk currently appears in the Web series "Border Patrol," which premiered in June 2008 on Atom.com. In 2009 Lenk appeared as a guest star on Nip/Tuck.
Besides acting, Lenk is a singer and playwright. He has toured with the European cast of Grease and has written three plays. Lenk took over the role of Franz in the Broadway musical Rock of Ages as of September 14, 2009, having originated the role in the Las Vegas and Los Angeles productions in 2006. Lenk frequently posts video blogs of himself on YouTube summing up his latest experiences on Broadway, the videos are usually called 'Tom's Broadway Blogs'.
He appeared in commercials for Pepsi Max. Lenk also appeared in an episode of Psych that poked fun at Buffy the Vampire Slayer (original Buffy actress Kristy Swanson appears in the episode).
Lenk performed in the June, 2012 edition of Don't Tell My Mother! (Live Storytelling), a monthly showcase in which authors, screenwriters, actors and comedians share true stories they would never want their mothers to know.
He is openly gay.