It's the latest in a string of defeats for NFP member Pio Tikoduadua, who said he was attacked by Frank Bainimarama on 9 August.
Footage leaked days after Mr Tikoduadua made the claims showed the prime minister grabbing and shoving him.
But Parliament's privileges committee cleared Mr Bainimarama of assault, and Mr Tikoduadua was suspended for six months after refusing to apologise for verbally abusing the prime minister in the House.
In a statement, Director of Public Prosecutions' Christopher Pryde said no action was needed because Parliament had "the power to discipline members of Parliament" and it had already accepted the committee's decision.
"As the altercation occurred within the precincts of Parliament, the Speaker exercised his authority and referred the matter to the Privileges Committee to hear evidence of the matter and to make findings on the allegation.
"Those findings were accepted by Parliament, which then endorsed and implemented a penalty."
It would not be in the public interest for another hearing to take place before the courts, he said.
"Had the matter not been heard by the Privileges Committee and dealt with by Parliament, there was sufficient evidence for the matter to proceed to court," he said.
The matter was now "closed".
Two Parliamentary staffers who filmed the video which leaked were forced to resign last month.