Joshua grew up in California and Seattle until age 8, when he moved back to Vancouver with his mother and younger sister. Soon after he took up acting, landing a role in a commercial for Keebler's Potato Chips. He is best known for the role of Pacey Witter on Dawson's Creek, but he has also appeared in several movies including Cruel Intentions, The Mighty Ducks series, Apt Pupil, Scream 2, The Laramie Project and The Skulls. In 2005 he was one of the few actors to be considered for the role of Bruce Wayne/Batman in "Batman Begins". He will next appear in the all-star ensemble drama Bobby, directed by Emilio Estevez, Joshua's co-star from The Mighty Ducks.
Joshua is left-handed and is 6 foot 2. Joshua dated two of his Dawson's Creek co-stars: actress Katie Holmes in 1998, and actress Brittany Daniel in 1999-2000. Joshua also dated Rosario Dawson and has currently been spotted kissing Diane Kruger whilst on vacation in Paris.