Lawyers for French investigative journalists Eric Laurent and Catherine Graciet argued unsuccessfully that tapes of conversations between them and a Moroccan official were inadmissible.
“It's a very big victory,” Patrice Spinosi, a lawyer for the king told AFP.
“There is no longer any obstacle to going ahead to conviction.”
Laurent, 69, and Graciet, 42, were charged with blackmail and extortion for demanding three million euros from Moroccan King Mohammed VI not to bring out a book purportedly containing damaging revelations about him.
They were arrested in Paris in August 2015 after a secretly recorded meeting with a Moroccan official at which they allegedly accepted payments of 40,000 euros each, a source close to the French investigation told AFP.
They were in possession of 80,000 euros in cash as they left the meeting, which occurred after the monarch had filed a case with Paris prosecutors.
The Moroccan government claims that the payment was the first instalment of a total of two million euros demanded by the authors in exchange for not publishing their book.
The journalists allegedly demanded three million euros initially, but reduced the figure after further negotiations. They deny the charges.
Laurent and Graciet published a highly critical book on Mohammed VI in 2012 titled “The Predator King” about his extensive business dealings which was banned in Morocco.
Their new book had been slated for publication in early 2016.
Laurent was previously recorded during two other meetings with the envoy, Hicham Naciri, a lawyer.
In an earlier preliminary hearing, the court judged the recordings were made with the “indirect participation” of French investigators “without the consent” of the two journalists, which it said contravened the principle of a fair trial.
But on Friday the court delivered its final ruling, saying police had played a “passive” role and could not be considered to have been “truly involved” in the bugging.
Investigating magistrates must now decide whether to send the case to trial or throw it out.