The Federal Criminal Court found Ousman Sonko guilty on several counts of intentional homicide, torture and false imprisonment.
A Swiss court on Wednesday convicted a former government minister from Gambia of crimes against humanity under former dictator Yahya Jammeh and jailed him for 20 years.
The Federal Criminal Court found Ousman Sonko guilty on several counts of intentional homicide, torture and false imprisonment.
Sonko, who was dismissed as Gambia's interior minister in 2016, was acquitted of rape.
"In its verdict ... the trial chamber found Ousman Sonko guilty of multiple counts of intentional homicide, multiple counts of torture and multiple counts of deprivation of liberty, each as a crime against humanity," the court said in a statement.
"The Trial Chamber concludes that Ousman Sonko committed these crimes.... as part of a systematic attack against the civilian population."
The judgment can be appealed.
Sonko is the highest-ranking official ever to be tried in Europe using universal jurisdiction which allows the most serious crimes to be prosecuted anywhere.
Geneva-based campaign group TRIAL International filed the original criminal complaint against Sonko and supported the plaintiffs.
Sonko fell out with Jammeh in the final months of his 22-year repressive rule before the latter was forced to flee in January 2017 after an election defeat. That same month, Sonko was arrested in Switzerland while seeking asylum.
Switzerland's public prosecutor had sought the maximum penalty of life imprisonment.
"The conviction of Ousman Sonko, one of the pillars of Yahya Jammeh’s brutal regime, is a major step on the long road to justice for Jammeh's victims," Reed Brody, a war crimes prosecutor attending the trial, told Reuters.
"The long arm of the law is catching up with Yahya Jammeh’s accomplices all around the world, and hopefully will soon catch up with Jammeh himself."
The case is Switzerland's second ever civilian trial for crimes against humanity and the Bellinzona court heard details between January and March of charges of rape, torture and murder allegedly committed between 2000-2016 either by Sonko or under his watch.
Sonko denied the charges and accused the plaintiffs of lying while denouncing his seven-year pre-trial detention - a period he said was partly spent in solitary confinement and affected his health.