Mr McMaster signed the bill on Friday, two days after the state Senate agreed to changes made to the bill by the statehouse.
The new law comes after conservatives pushed for the legislation earlier this year, responding to hesitancy by drug companies to provide products to states looking to use them during lethal injections.
This reluctance from drug companies has meant that South Carolina has not been able to get the drugs needed to perform a lethal injection for several years.
According to The State, the previous state law meant that lethal injection was the default method of execution in the state, and if an inmate selected that method, an execution could not be done in another way. This led three inmates to receive stays of execution.
The new law dictates that an inmate must choose between firing squad, the electric chair, or lethal injection. But if the drugs necessary for the injection are unavailable, the inmate would be forced to choose between the other two methods. If no choice is made, electrocution would be the method used.
The South Carolina Department of Corrections is currently ready to perform an execution using the electric chair, but still needs to figure out how firing squad executions would work in the state, according to the department’s director of communications Chrysti Shain.
Ms Shain said the department “continually trains to perform these duties,” in relation to the electric chair, making checks on a regular basis to ensure it’s ready for use.
The method of firing squad, on the other hand, has never been used before in the state and no system is in place for how it would work.
But now that the bill has been signed into law by the governor, the Department of Corrections will create a policy for how this method of execution will be used.
“We would look for guidance from other states and the courts as to what has been deemed constitutional,” Ms Shain told The State. She added that at the moment there’s no timeline for when the department expects to be ready to perform this kind of execution.
South Carolina state rep Justin Bamberg, a Democrat, questioned during the debate about the law if changing the penalty an inmate might face after they’ve already been sentenced is constitutional.
“With the law as it was written at the time, these individuals made a decision – do I plead guilty or take, maybe, a life sentence... or do I go to trial and risk death?” he said on the floor of the statehouse. “And if I do go to trial, what kind of death am I facing?”
Mr Bamberg argued that both lawyers and inmates could have made other decisions during their trials if they were aware that the only execution methods were the electric chair and firing squad.
The state representative tried to remove the part of the bill that was retroactive but failed to do so.
“It’s not right,” he said. “It’s not constitutional. We don’t need to do it.”
“We cannot change the rules of the game after the game has been played and there is a winner and a loser,” he added.
Republican state senator Greg Hembree admitted on Wednesday that the new law will probably attract lawsuits.
“If we pass the bill, the very first execution we have is going to be litigated probably to the United States Supreme Court,” he said.
Speaking to MSNBC, Mr Bamberg said: “It blows my mind to see my state heading backwards. We started the death penalty using the electric chair back in 1912. Since that time, unfortunately, out of the 282 executions that this state has had, a majority of them, almost 74 per cent, have been African American males, even though African Americans only make up 37 per cent of the population in this state.”
“Inmates have a choice... but not really, there’s no humane way to kill a human being. I don’t view the firing squad any better than the electric chair, lethal injection or otherwise. The firing squad is something they do in North Korea, think about that,” Mr Bamberg added.
The Independent has reached out to the office of the governor for comment.