Smith was born in Cedar Rapids, Iowa to parents who owned a horse ranch. He was discovered at a local mall in his hometown by a local talent scout to fly to New York City to compete at the International Modeling and Talent Association (IMTA) Convention. Smith was signed on to a Tommy Hilfiger modeling campaign. He used the money he earned to pay for his acting classes. Three months later, Smith flew to Los Angeles to do a screen test for the 1998 WB pilot Minor Threat. He landed his first audition for a network pilot and soon moved to Los Angeles. The pilot was not picked up.

He has gone on to do eight prime time network pilots, more than a dozen guest-starring roles and three series. He appeared in the films Eight Legged Freaks, Not Another Teen Movie, Radio, New York Minute and the Sundance Grand Jury nominee Weapons. He had a recurring roles in the Emmy-nominated CBS series Joan of Arcadia, the highly acclaimed Emmy Fox show 24 season 3 as Kyle Singer, the short-lived WB series Summerland and the acclaimed Judd Apatow creation for NBC Freaks and Geeks. He was also a main cast member in the short lived fox show Drive. Riley also played Dean Talon in the Disney Channel movie Motocrossed. He played a love interest and mentor to Andy Carson on the race track.

He played Russ, the love interest of Mary Elizabeth Winstead's character in the dancing film Make it Happen.

In 2009 he appeared one episode on a paranormal TV series starring Jennifer Love Hewitt Ghost Whisperer.