"The NPA can take another decision to discontinue [the matter]. [It has to decide] because right now there is a decision to prosecute and an indictment will to be served," he said.
"If it wants to stop the prosecution, it's going to have to make a decision not to [go ahead]."
However, the NPA would have to prove that the decision it was making was a rational one, Grant said.
"There is always a discretion on the part of the NPA to discontinue a prosecution; that discretion has to be exercised in accordance with, at the very least, the rule of law in the Constitution, and that's why we saw the references to rationality today.
"The criteria posed by the rule of law is that decisions must be taken rationally," he said.
Earlier the High Court in Pretoria handed down a judgment in the so-called Spy Tapes matter.
Deputy Judge President Aubrey Ledwaba ruled that the decision to discontinue the prosecution against Zuma should be reviewed and set aside.
The full bench of the court found Zuma should face the 783 charges of corruption.
In September 2008, in the KwaZulu-Natal High Court in Pietermaritzburg, Judge Chris Nicholson dismissed criminal charges against Zuma, citing a political conspiracy to influence the case by former president Thabo Mbeki and others.
Nicholson's decision was taken to the Supreme Court of Appeal and overturned.
Zuma subsequently appealed this in the Constitutional Court, setting in motion a direct approach to the NPA to make written and oral representations on why the case should be dropped.
On April 6 2009 then-NPA head Mokotedi Mpshe said recordings of telephone conversations between then-Scorpions boss Leonard McCarthy and former NPA boss Bulelani Ngcuka showed political interference in the decision to charge Zuma.
The two were recorded discussing the timing of bringing charges against Zuma. The charges related to his alleged involvement in the country’s multibillion-rand arms deal.
Zuma’s former financial adviser Schabir Schaik was found guilty of fraud and corruption by the KwaZulu-Natal High Court in Durban in June 2005. He tried to solicit a bribe for Zuma from a French arms company involved in the deal.
On April 7 2009 the charges against Zuma were withdrawn in the High Court in Durban.
Zuma was sworn in for his first term as president in May that year, following general elections.
According to Grant, the best thing for Zuma to do would be to appeal the court's finding, however, this would not be an easy task.
"If I were him, I would do everything that I could to try to postpone having to deal with this, so given that he's got a lot of resources, he may well use those."
He said it would, however, be difficult for Zuma to appeal as the judgment was, in his opinion, well-reasoned and based on facts.
"The court was purely aware of the importance of this judgment today, it was a unanimous judgment."
Grant said, in its judgment, the court had found that the NPA had not only acted irrationally on one point but on a number of bases.
"It was irrational for many reasons, so it is going to be a tough one to appeal in my view. I would be surprised if the Supreme Court of Appeal or the Constitutional Court even hears an appeal," he said.
The court's judgment had affirmed three things in Grant's opinion.
First, it had affirmed the NPA's right to decide on whether to prosecute on a matter or not granted the decision to do so was a rational one; second it had affirmed that the NPA was obligated to treat all cases equally; and finally, the NPA could not rely on an abuse of power to make decisions regarding a prosecution.
"It may of course raise this and be concerned about it, but ultimately it may not take a decision on the basis of an abuse of power, it must wait for a court to decide that," Grant said.
"Those are the three things that I got out of the judgment."