Judges at the Berlin court said the 47-year-old Czech-Vietnamese national, identified as Long N.H., was guilty of aiding an abduction and working for a foreign intelligence service.
But they handed him a relatively mild sentence of three years and ten months after he confessed to his involvement.
"The accused knew of the plans of the Vietnamese secret service, but did not belong to the top level of command," judges said in their verdict, according to DPA.
Long N.H. admitted during his trial that he rented the vehicle used in last July's abduction of fugitive Vietnamese state company official Trinh Xuan Thanh, who was spirited back to Hanoi.
Thanh - also a Communist party functionary who was seeking political
asylum in Germany - has since been sentenced to two life terms in Vietnam on corruption charges.
The 52-year-old and his companion were walking in Berlin's Tiergarten park when they were dragged into a van in broad daylight and smuggled back to Vietnam.
The German government was outraged, calling it a "scandalous violation" of its sovereignty.
Communist-ruled Vietnam has always insisted that Thanh, the former head of PetroVietnam Construction, returned voluntarily to face embezzlement charges.
Thanh's German lawyer, Petra Schlagenhauf, has described the kidnapping as
"like a story from the Cold War".
Long N.H., was once among thousands of so-called guest workers in communist East Germany. He was later denied asylum and resettled in Prague.
He was arrested there last August and extradited to Germany days later.
He admitted renting the van used in the abduction in Prague and driving it to Berlin, but he was not at the wheel during the kidnapping. He then drove the van back to Prague.
It remains unclear exactly how Thanh was transported back to his home country, but investigators believe he was driven to the Slovakian capital Bratislava and then flown to Hanoi.
German media have reported that a Slovakian government plane lent to a visiting Vietnamese delegation at the time was involved in the transfer.
Slovakia has said it noticed nothing suspicious about the delegation or their flights, but warned Hanoi of harsh consequences if the allegations proved true.