The court in the eastern town Kankan on Monday recommended the defendants serve a minimum of 30 years for the January 2018 shooting.
All but one of the 13 were sentenced in absentia - 12 are suspected to have fled abroad.
"The ringleader, Moussa Kante, was the only one who was in court, pleading not guilty," Judge Kpoulomou Gbamon told AFP.
The preacher, Abdul Aziz Tuwaijri, was shot dead in the village of Kantebalandougou, near the border with Mali and Ivory Coast.
He was on a mission to build mosques and spread the conservative Wahabi form of Islam in Guinea, a country where Islam, the predominant religion, is traditionally moderate and often incorporates animist beliefs.
A security official at the time said that, according to preliminary inquiries, the Saudi had staged a sermon "that went down badly with some of the local people, notably traditional hunters, who staged an ambush" of him.
The source was unable to give further details about the sermon.
A local person who had been driving the preacher around on his motorbike was seriously hurt in the attack.
Guinea and Saudi Arabia enjoy prospering bilateral relations.
Guinean President Alpha Conde was part of an official delegation of Muslim leaders who travelled to Saudi Arabia during a visit by US President Donald Trump in May.
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