Nahid Hattar, a Christian, was hit by three bullets outside the court in the capital Amman where he was standing trial, state news agency Petra said.
Mr. Hattar’s killer was arrested and police are investigating the killing, TV reports said.
The writer was detained in August for 15 days on charges of insulting God.
The cartoon he shared depicts a bearded man lying in bed with two women and smoking, asking God to bring him a drink.
Mr. Hattar was attacked on social media for being anti-Islam.
He said he had not meant to cause offence and wanted to expose radical Islamists’ view of heaven.
But the authorities said he had broken the law by sharing the cartoon.