Please don't kill me.
Josh Wheaton (Shane Harper), a Christian college student, enrolls in a philosophy class taught by Professor Jeffrey Radisson (Kevin Sorbo), an atheist, who demands that his students sign a declaration that "God is dead" to get a passing grade. Josh is the only student in the class who refuses to sign and is then required by Radisson to debate the topic with him, with the class members deciding who wins.
Radisson's girlfriend, Mina (Cory Oliver) is a Christian whom he often belittles in front of his fellow atheist colleagues. Her brother Mark (Dean Cain) is a successful businessman and atheist who refuses to see their mother, who suffers from dementia. Mark breaks up with his girlfriend, Amy (Trisha LaFache), a left-wing blogger, when she is diagnosed with cancer. A girl named Ayisha (Hadeel Sittu), whose family (especially her father) are strongly devout Muslims, is secretly Christian; when her father discovers this, he throws her out.
Radisson gives Josh 20 minutes at the end of the first three lecture sessions to argue that God exists. In the first two debates, Radisson has counter arguments for all of Josh's points. Josh's girlfriend Kara (Cassidy Gifford) breaks up with him, fearing that standing up to Radisson will jeopardize their academic future. Ultimately, it comes down to the third and final debate between Radisson and Josh, who again both make compelling points. Josh then halts his line of debate to pose a question to Radisson: "Why do you hate God?" After Josh repeats the question twice more, Radisson explodes in rage, confirming he hates God for his mother's death that left him alone despite his prayers. Josh then casually asks Radisson how he can hate someone that doesn't exist. In the end, Martin (Paul Kwo), a foreign exchange student whose father had encouraged him not to convert to Christianity, stands up and says "God's not dead." Almost the entire class follows Martin's lead, causing Radisson to leave the room in defeat.
After the final debate, Josh invites the newly born-again Martin to attend the Newsboys concert that is in town. Radisson reads a letter from his late mother, and is moved to reconcile with Mina. Amy confronts the Newsboys in their dressing room, only to admit that she wants to get to know God. While on his way to find her, Radisson is struck by a car and fatally injured. Reverend Dave (David A. R. White) finds him and guides him in becoming a born-again Christian as he takes his last breath. Mark taunts his mother, who turns the tables on him and tells him that the devil has helped him to succeed, to keep him from turning to God. Before the final song, the Newsboys play a video clip of Willie Robertson congratulating the 'young man' who successfully defended God against his professor. The Newsboys then play their song "God's Not Dead", dedicating it to the same person Robertson commended.