Abe, 67, immediately collapsed after being shot in the neck and was rushed to the hospital.
The ex-leader had no vital signs and was bleeding heavily, hospital officials said. He was pronounced dead about five hours later.
The suspected attacker – reported to be a male in his 40s – was tackled at the scene and arrested.
Abe – in office from 2006-07 and 2012-20 – remains the country’s longest-serving PM and best-known figure internationally.