The hostage situation ended when French police shot the two attackers, but not before one of the knifemen slit Hamel's throat, killing him.
A special French police unit confronted the attackers as they left the church, shooting them dead, and freeing three hostages, physically unharmed.
Further, some reports quoted locals around the area as stating, "A third nun escaped and raised the alarm, and anti-terrorists officers were on the scene within minutes".
A spokesman for the Interior Ministry in Paris explained that the two men entered through the back door of the church, just after 9:00 a.m.
French President Francois Hollande has called Pope Francis to express his "chagrin".
Police arrested at least one person in an initial sweep following the attack.
This will be the sixth "known wolf" terror attack targeting France in the past two years.
The identity of the other assailant has not yet been revealed.
Molins identified one of the attackers as Adel Kermiche, who'd been caught trying to reach Syria, base of operations for ISIS, twice a year ago.
France is now on high alert after the July 14 truck attack in Nice that left 84 people dead.
He was released and fitted with an electronic bracelet that allowed him to leave his house on weekdays between 8:00am and 12:30pm, Mr Molins said.
She said the attackers recorded themselves, adding: "They did a sort of sermon around the altar, in Arabic".
In April 2015, Algerian national Sid Ahmed Ghlam was arrested in Paris on suspicion of planning to attack churches in the capital. And that's when the tragedy happened. This was the first attack inside a French church in recent history.
French president François Hollande called for religious unity and pledged to meet religious leaders including Christians, Muslims and Jews to resist efforts to divide French society.
French lawmakers approved a six-month extension of emergency rule after the July 14 attack while the Socialist government also said it would step up strikes against Islamic State in Iraq and Syria.
The attack is the latest in a string of deadly assaults in Europe, including the mass killing in Nice, southern France, on Bastille Day and four incidents in Germany.