The group was detained in August near Nicaragua's border with Honduras while traveling in six vans with logos like those used by Mexican television giant Televisa. The bundles of cash had been stashed in compartments inside the vehicles.
Judge Edgard Altamirano said evidence showed the 17 men and one woman were members of organized crime.
"The way they stashed the cash in the vehicles with the Televisa logos, the large amount of money, that's the typical way members of organized crime act," Altamirano said.
The detainees told authorities at the time they were members of a Televisa news crew that had traveled to Nicaragua to cover the trial of suspects linked to the 2011 killing of Argentine folk singer Facundo Cabral.
Authorities haven't said whether the group, which was led by Raquel Alatorre, was working for a drug cartel. Several were identified as employees of private security firms in Tamaulipas, the northern Mexico border state that is home to the Zetas and Gulf cartels.
Before Altamirano issued his verdict, he allowed the defendants to speak.
Only eight of the defendants, looking distraught, spoke and asked the judge for a "fair decision" and said they were not guilty. They also apologized to Nicaragua and Mexico for any inconvenience their case caused.
Alatorre spoke first and asked that she be transferred from a prison in the capital to a women's prison in southwest Nicaragua.
Alatorre's attorney, Ricardo Ramirez Magnali, said the prosecution didn't prove its case but he wouldn't say whether his client plans to appeal the verdict.
"The prosecution did not prove that the defendants came to alter our Nicaraguan financial system with money laundering," Ramirez Magnali said.
Prosecutors said it was Alatorre who processed the group's migration permits, and arranged for lodging and food. They said she had crossed into Nicaragua several times since 2008. They said she entered and exited Nicaragua 22 times between 2010 and 2011.
Nicaraguan authorities said the elaborate ruse was intended to smuggle the cash through Nicaragua to the neighboring nation of Costa Rica to the south.
Mexican drug cartels frequently buy Colombian cocaine to ship north to the U.S. market, and often must smuggle cash back south to pay the Colombia suppliers.
Prosecutors requested the maximum sentence of 30 years. Altamirano set the sentencing date for Jan. 18.