Only two (2) states, Maine and Vermont, allow felons to vote from prison. Other U.S. states may permanently ban felons from voting even after they have been released from prison, parole, probation, and/or completely have served all their required punishment or paid all of their fines.
Pointedly, in Maine and Vermont, felons never lose their right to vote, even while they are incarcerated. In Florida, Iowa and Virginia, felons and ex-felons permanently lose their right to vote. Virginia and Florida have supplementary programs which facilitate gubernatorial pardons. The remaining U.S. states each have their own approaches to the issue.
Overall, in 38 states and the District of Columbia, most ex-felons automatically gain the right to vote upon the total completion of their sentence. In some states, ex-felons must wait for a certain period of time after the total completion of their sentence before voting rights can be restored. And, in some states, an ex-felon must apply to have their voting rights restored.
As a suggestion, any convicted felon seeking information on the process to regain voting rights needs to contact an election official in the jurisdiction where he or she wishes to register and vote.