Is of Irish descent. He has English, Scottish, and German ancestry.
Harris was born in Albuquerque, New Mexico, and grew up in Ruidoso, New Mexico (a small town 120 miles south of Albuquerque). His parents, Sheila (Scott) and Ron Harris, ran a restaurant. He attended La Cueva High School in Albuquerque, where he acted in school plays and musicals. Harris graduated as an honors student in 1991.
Harris is openly gay, confirming this in November 2006 by saying "I am happy to dispel any rumors or misconceptions and am quite proud to say that I am a very content gay man living my life to the fullest and feel most fortunate to be working with wonderful people in the business I love."
Harris attended the Emmy awards in September 2007 with his partner David Burtka, later confirming the relationship, which he said began in 2004 in an interview on The Ellen DeGeneres Show. On August 14, 2010, Harris announced that he and Burtka were expecting twins via a surrogate mother. The fraternal twins Gideon Scott, a boy, and Harper Grace, a girl, were born on October 12, 2010.
Following the passage of the Marriage Equality Act in New York on June 24, 2011, Harris and Burtka announced their engagement via Twitter, stating that they had proposed to each other five years ago but kept the engagement secret until same-sex marriage became legal.