The 37 year old met the The Twilight Saga: Eclipse beauty in late 2011 and the couple has reportedly been dating ever since.
A source tells Us Weekly magazine, "He thought she was gorgeous. There was an instant attraction. He has a couple of scripts in the works and she writes as well, so they have a lot to talk about."
The two were snapped arm-in-arm in Hawaii last week (13Jun12) at the Maui Film Festival, where he was honoured with the Triple Threat Award, and it appears the relationship is still going strong.
A friend adds, "She's really intelligent... That was a huge thing for Josh, because he's always complaining about how girls in Hollywood only care about glitz and glamour."
Radnor was last linked to actress Lindsay Price.