Became known for his role as Leonard Hofstadter on the CBS sitcom The Big Bang Theory and as David Healy on hit sitcom Roseanne.
He was raised by a marriage councilor mother and a rehabilitation instructor father and made his acting debut at age 12 in the 1987 mini-series Murder Ordained.
He appeared as Rusty Griswold in the 1989 film National Lampoon's Christmas Vacation and, in 2011, he made a guest appearance on Entourage as himself.
He began dating actress Kelli Garner in 2011, but the couple split in 2014. In 2018, he began dating Alaina Meyer. They welcomed a son in December 2019.
He dated his Big Bang Theory co-star and love interest, Kaley Cuoco, for two years while on the show.