Not sure just when it began, but by 1968 it became Federal law.
The actual term is "disenfranchisement." It dates back to ancient times, and the original idea was that conviction of a felony removed all
rights from the offender. In medieval Europe, the offender could even be killed by his neighbors without recourse.
There's some suggestion that the term "outlaw" in early American practice meant the same thing. The idea was total ostracism without getting our hands bloody.
I'd really like to think we have a more modern view of crime and punishment as a society, but here we are.