For more than a decade, Juan Orlando Hernández wielded power in Honduras, first as a member of Congress, then as that body’s leader and finally as the nation’s president.

On Friday, an American jury in Federal District Court found Mr. Hernández guilty of conspiring to import cocaine into the United States and of possessing and conspiring to possess “destructive devices,” including machine guns.

After the verdict was delivered, Mr. Hernández, who faces a mandatory prison term of at least 40 years and is scheduled to be sentenced on June 26, rose to his feet and stood quietly with folded hands as the jurors filed from the courtroom.

During his first presidential campaign in 2013, Mr. Hernández, a member of the right-wing Honduran National Party, portrayed himself as a law-and-order candidate who could stem the epidemic of drugs and crime that had suffused the country.

But according to prosecutors in the United States, Mr. Hernández was allied with the same forces he purported to oppose. A string of witnesses testified during a conspiracy trial in Manhattan that Mr. Hernández’s political success was fueled by drug proceeds funneled to him by cocaine traffickers whom he treated as business partners.

Prosecutors have said that Mr. Hernández received millions of dollars from trafficking organizations in Honduras, Mexico and elsewhere, including from Joaquín Guzmán Loera, known as El Chapo, who was a Mexican drug lord and the former leader of the Sinaloa Cartel. In return, prosecutors added, Mr. Hernández allowed vast amounts of cocaine to pass through Honduras on its way to the United States.