"Cristina is alive because, for reasons that have yet to be technically confirmed, the gun containing five bullets did not fire despite the trigger being pulled," Argentina's President Alberto Fernandez said in a speech to the nation.
"This is the most serious event that has occurred since we restored democracy in 1983," according to Fernandez.
Footage from the incident showed the man pointing a handgun at Kirchner, who led the country from 2007 to 2015 and is now facing corruption charges.
The incident occurred in Buenos Aires' upscale Recoleta neighborhood.
"I saw this arm come up over my shoulder behind me with a gun, and with people around me, he was subdued," an unidentified Kirchner supporter told AFP.
Security Minister Anibal Fernandez stated that a suspect was apprehended on Thursday night, but that investigators needed to examine the crime scene and circumstances surrounding the incident.
According to local media, the suspect was a 35-year-old Brazilian national.
President Fernandez declared Friday a public holiday to allow people to "express themselves in defense of the life of democracy and in solidarity with our vice president."