Speaking after Thursday's floor session, Hall said it took him a while to make up his mind about the reform bill.
"As late as last night I might have voted 'no,'" he said.
He said conversations with law enforcement, including Putnam County Prosecutor Mark Sorsaia, helped to change his mind
"I don't think public safety's being compromised," he said. "I think public safety is enhanced by doing that."
Sen. Clark Barnes, R-Randolph, called the prison reform bill a "step in the right direction."
Barnes sits on the Legislature's Oversight Commission for Jails and Prisons.
"We have month after month sat and heard the statistics," he said. "We have problems. We have problems that, basically, this bill doesn't touch. But we have to do something.
"This is a step in the right direction and I urge my fellow members to join me in a vote 'yes' for this bill."
The bill is likely to be much more contentious once it comes up for a debate in the House of Delegates. Republicans there have routinely criticized the Justice Reinvestment Initiative's recommendations.
House Minority Leader Tim Armstead, R-Kanawha, has said the early-out provision for non-violent offenders would be a major sticking point in his support of the bill.
He said the bill's definition of "nonviolent offenders" is too vague, and the legislation provides no oversight on which prisoners may be released early.
"This is just a random way of saying we want to clear out our jails so we're going to let people out of jail early," he told the Daily Mail last month. "These are people that have not been granted parole. We have a parole process in place that looks at whether or not someone is able to go out into society.
"If they are eligible to be released early, why haven't they been released under the parole process?"
The law defines nonviolent offenders as "a person who is not serving a sentence for a crime of violence against the person, a felony offense involving the use of a firearm or a felony offence where the victim was a minor child."
Delegate Patrick Lane, R-Kanawha, head of the House's GOP caucus, has said he believes prisoners should have to serve their entire sentences before being released into a supervisory program.
Speaking to the Daily Mail in January, Lane cautioned against releasing prisoners just because keeping them incarcerated is costing the state money.