Tenney was born in Princeton, New Jersey to a psychiatrist mother and a research physicist father.

He was married to actress Teri Hatcher from 1994 to 2003. They have one daughter, Emerson Rose Tenney, born in November 1997.

He received his B.A. degree from Vassar College, where he majored in drama and philosophy. He then studied at Juilliard, after which he made his professional debut starring in a touring production of The Real Thing directed by Mike Nichols. This led to his working steadily on and off-Broadway, as well as in regional theater. His New York City stage credits include Biloxi Blues, The Substance of Fire, and The Heiress.

Tenney's work in television includes a lead role in the short-lived Steven Bochco series Brooklyn South, the Kristin Chenoweth sitcom Kristin and guest appearances on Will & Grace, Murphy Brown, Spenser: for Hire, and Get Real. He currently co-stars as Kyra Sedgwick's husband on the TNT crime drama The Closer. Also, he is playing Dr. Simon, the love interest of Sally Field's character Nora Walker on Brothers & Sisters.

He appeared as Matthew Perry's best friend in Fools Rush In. Tenney has appeared in the following films in small roles: Tombstone, Nixon, Music from Another Room, and the 2009 remake of the horror film The Stepfather. He also appears in the John Cameron Mitchell film, Rabbit Hole.

Tenney will portray Martin Jordan in the upcoming 2011 superhero film Green Lantern.