Hephner was born in Madison Heights, Michigan, to Tom and Patti Hephner, and grew up in the small town of Sand Creek, located in southern Michigan near Adrian. Hephner was athletic growing up, playing basketball and football, and he graduated from Sand Creek High School. Hephner was named to the academic all-state team for Class C-D for the 1993–1994 season.
Hephner began his Hollywood career with small roles in two feature films: in the war drama Tigerland (2000), starring Colin Farrell and the romantic comedy-drama Maid in Manhattan (2002), starring Jennifer Lopez and Ralph Fiennes, where he played a room Service waiter. Also in 2002, he starred in two short films, The Outlands and So How Do You Feel About Your Watch.
After starring in the short-lived Fox legal drama The Jury as Keenan O'Brien in 2004, in 2005, he guest-starred in the NBC legal drama Law & Order: Criminal Intent in season 4: episode 21 titled "The Unblinking Eye" as Michael Pike.
Hephner starred as author Pat Conroy in the Hallmark Hall of Fame TV movie The Water Is Wide (2006) with Alfre Woodard, based on Conroy's book and a remake of the drama Conrack (1974), starring Jon Voight.
He starred as Morgan Stanley Buffkin in The CW comedy-drama Easy Money. The show aired for four episodes in October 2008 before it was cancelled and the other four episodes already filmed aired in mid-2009.
In 2010, Hephner replaced Ben Browder in a recurring role in the short-lived CW comedy-drama Hellcats as Red Raymond, a football coach and the former flame of Hellcats' coach Vanessa Lodge (Sharon Leal).
From 2011 to 2012, Hephner co-starred with Kelsey Grammer as Ben Zajac in the Starz political drama Boss.
From 2013 to 2014, Hephner had a recurring role in the second season of the NBC drama Chicago Fire as Jeff Clarke, a firefighter and a former U.S. Marine.
In 2015, Hephner co-starred with Sharon Stone in the short-lived TNT action drama Agent X as John Case, a former Special Forces operator, who becomes "Agent X".
From 2016 to 2017, Hephner reprised his role as Jeff Clarke in Chicago Fire's medical spinoff Chicago Med, where Clarke returns to medical school. He appeared in the first season finale and recurred in the show until towards the end of the second season.
