London investigators first ruled that Calvi committed suicide but his family pressed for further investigation and eventually murder charges were brought against the five defendants.
Calvi's bank collapsed after loans worth $1.3bn were made to several dummy companies in Latin America, accompanied by letters of credit from the Vatican.
While denying any wrongdoing, the Vatican bank agreed to pay $250m to Ambrosiano's creditors in one of Italy's biggest fraud cases.
One defendant, Giuseppe "Pippo" Calo, is already serving a life sentence on convictions 20 years ago on Mafia charges.
The other defendants were Calvi's driver and bodyguard, Silvano Vittor, businessman Flavio Carboni, another businessman, Ernesto Diotallevi, and Carboni's former girlfriend, Austrian Manuela Kleinszig.
|Calo followed the court proceedings via|
video link from his prison [Reuters]
Judge Mario D'Andria at the start of the trial in October 2005 urged the court to keep in mind that it involved facts from nearly a quarter of a century ago.
New forensic tests in 2003 on Calvi's shoes found no traces of paint or metal from the scaffolding under the bridge, indicating he did not climb it but was killed elsewhere and his body later hung from the bridge.
None of the five defendants was accused of physically killing Calvi.
Calo followed the verdict by video camera from a prison in central Italy while the other four chose not to attend the hearing in the largely empty high-security courtroom, which is permitted under Italian law.
Dario Piccioni, a lawyer for the Calvi family, said Calvi's widow was dead and a son who lives in Canada was not immediately informed about the verdict.
The lawyer hinted at a fresh trial saying the jury had not ruled out foul play.