She gained fame for portraying Bridget Hennessy on the ABC sitcom 8 Simple Rules. In 2007, she began playing Penny on The Big Bang Theory.
When she was growing up, she became a nationally-ranked amateur tennis player and she made her debut at Karin in the 1995 film Virtuosity.
She appeared in the 2007 film To Be Fat like Me and the 2014 film Authors Anonymous.
She was engaged to Josh Resnik for six months starting in October of 2011, but they broke off the engagement in 2012. She was then married to Ryan Sweeting from 2013 to 2015. In 2016, she began dating Karl Cook. Her sister Briana competed on The Voice in 2013.
She starred in the hit show The Big Bang Theory, which was created by Chuck Lorre.