Gelli was born in Pistoia, Tuscany. During the 1930s, Gelli volunteered for the Blackshirts expeditionary forces sent by Mussolini in support of Francisco Franco's rebellion in the Spanish Civil War. He participated in the Italian Social Republic with Giorgio Almirante, founder of the neofascist Italian Social Movement (MSI). After a sales job with the Italian mattress factory Permaflex, Gelli founded his own textile and importing company.
In 1970, during the failed Golpe Borghese, he was delegated the role of arresting the Italian President, Giuseppe Saragat. As Master of the Propaganda Due (P2) lodge, Gelli had ties with very high level personalities in Italy and abroad, in particular in Argentina, where he was a fugitive for many years. The Argentine Chancellor Alberto Vignes drafted with Juan Perón, who had returned from exile in 1973, a decree granting Gelli the Gran Cruz de la Orden del Libertador in August 1974, as well as the honorary office of economic counselor in the embassy of Argentina in Italy. Gelli publicly declared on repeated occasions that he was a close friend of Perón, although no confirmation ever came from South America. Gelli affirmed that he introduced Peron to Masonry and that this friendship was of real importance for Italy. He stated: "Peron was a Mason, I initiated him in Madrid in Puerta de Hierro, in June 1973."
According to a letter sent by Gelli to César de la Vega, a P2 member and Argentine ambassador to the UNESCO, Gelli commissioned P2 member Federico Carlos Barttfeld to be transferred from the consulate of Hamburg to the Argentine embassy in Rome. Gelli was also named minister plenipotentiary for cultural affairs in the Argentine embassy in Italy, thus providing him with diplomatic immunity. He had four diplomatic passports issued by Argentina, and has been charged in Argentina with falsification of official documents. During the 1970s, Gelli brokered three-way oil and arms deals between Libya, Italy and Argentina through the Agency for Economic Development, which he and Umberto Ortolani owned.
Several members of the Argentine military junta have been found to be P2 members, such as Raúl Alberto Lastiri, Argentina's interim president from July 13, 1973 until October 12, 1973, Emilio Massera, part of Jorge Videla's military junta from 1976 to 1978, and José López Rega, the infamous founder of the Argentine Anticommunist Alliance ("Triple A"). The lodge P2, also known as the Propaganda Due, was also linked to the robbery of Juan Peron's severed hands.
In 1990 a report on RAI Television alleged that the CIA had paid Gelli to instigate terrorist activities in Italy. Following this report, which also claimed that the CIA had been involved in the assassination of the Swedish Prime minister Olof Palme, then President Francesco Cossiga requested the opening of investigations while the CIA itself officially denied these allegations. Critics have claimed the RAI report to be a fraud because of the inclusion of testimony from Richard Brenneke, who claimed to be a former CIA agent and made several declarations concerning the October surprise conspiracy. Brenneke's background was also investigated by a U.S. Senate subcommittee, which dismissed Brenneke's claims of CIA employment.
Gelli's downfall started with the Banco Ambrosiano scandal, which led to a 1981 police raid on his villa and the discovery of the P2 covert lodge. On March 17, 1981 a police raid on his villa in Arezzo led to the discovery of a list of 962 persons composed of Italian military officers and civil servants involved in Propaganda Due (also known as "P2"), a clandestine lodge expelled from the Grande Oriente d'Italia Masonic organization. A list of alleged adherents was found by the police in Gelli's house in Arezzo in March 1981, containing 962 names, among which were important state officials, some important politicians and a number of military officers, including the heads of the three Italian secret services. Future Italian prime minister Silvio Berlusconi was on the list, although he had not yet entered politics. He was then known as the founder and owner of "Canale 5" TV channel, and was listed as a member of P2.
A Parliamentary Commission, directed by Tina Anselmi (of the Christian Democratic party), found no evidence of crimes, but in 1981 the Italian parliament passed a law banning secret associations in Italy. Gelli was expelled from GOI freemasonry on October 31, 1981, and the P2 scandal provoked the fall of Arnaldo Forlani's cabinet in June 1981
The P2 lodge had some form of power in Italy, given the public prominence of its members, and many observers still consider it to be extremely strong. Several famous people in Italy today (starting with the top TV anchor-man Maurizio Costanzo) were affiliated with P2. Among these Michele Sindona, a banker with clear connections to the Mafia, has been clearly associated with P2. In 1972, Sindona purchased a controlling interest in Long Island's Franklin National Bank. Two years later, the bank collapsed. Convicted in 1980 in the USA, "mysterious Michele" was extradited to Italy. Two years later, he was poisoned in his cell while serving a life sentence. The P2 membership list was authenticated, with a few exceptions, by a 1984 parliamentary report.
On the run, Gelli escaped to Switzerland where he was arrested on September 13, 1982 while trying to withdraw tens of millions of dollars in Geneva. Detained in the modern Champ-Dollon Prison near Geneva, he managed to escape and then fled to South America for four years. In 1984 Jorge Vargas, the secretary general of the Unión Nacionalista de Chile (UNACH, Nationalist Union of Chile, a short-lived National Socialist party ) and a former member of the Movimiento Revolucionario Nacional Sindicalista (National-Syndicalist Revolutionary Movement ), declared to La Tercera de la Hora that Gelli was then in Pinochet's Chile.
Finally, Gelli surrendered in 1987 in Switzerland to investigative judge Jean-Pierre Trembley. He was wanted in connection with the 1982 collapse of the Banco Ambrosiano and on charges of subversive association in connection with the 1980 Bologna railway station bombing, which killed 85 people. He was sentenced to two months in prison in Switzerland, while an Italian court in Florence sentenced him on December 15, 1987, in absentia, to 8 years in prison on charges of financing right-wing terrorist activity in Tuscany in the 1970s. Gelli had already been sentenced in absentia to 14 months in jail by a court in San Remo for illegally exporting money from Italy.
Switzerland eventually agreed to extradite him to Italy, but only on financial charges stemming from the collapse of Banco Ambrosiano. Gelli's extradition in February 1988 required a high-level security apparatus, including 100 sharpshooters, decoy cars, a train, road blocks and two armored cars to transfer him to Italy. In July 1988 he was absolved of charges of subversive association by a Bologna court but was presented with a five-year prison term for slander, having side-tracked the investigation into the 1980 bombing of the Bologna train station. Stipulations connected to his extradition, however, prevented him from serving time. Two years later, an appeal court threw out Gelli's slander conviction. A retrial was ordered in October 1993.
In 1992 Gelli was sentenced to 18 years and six months of prison after being found guilty of fraud concerning the collapse of Banco Ambrosiano in 1982 (a "black hole" of $1.4 billion was found). The Vatican bank, Istituto per le Opere di Religione, main share-holder of the Banco Ambrosiano, consequently had a "black hole" of $250 million. This sentence was reduced by the Court of Appeal to 12 years. The year 1992 also saw the beginning of the trial of 16 members of the P2 Masonic Lodge, which included charges of conspiracy against the state, espionage, and the revelation of state secrets. In April 1994 Gelli received a 17-year sentence for divulging state secrets and slandering the investigation, while the court threw out the charge that P2 members conspired against the state; Gelli's sentence was reduced, and he was placed under house arrest two years later.
In April 1998 the Court of Cassation confirmed a 12-year sentence for the Ambrosiano crash. Gelli then disappeared on the eve of being imprisoned, in May 1998, while being under house arrest in his mansion near Arezzo. His disappearance was strongly suspected to be the result of being forewarned. Then, finally, he was arrested in the French Riviera in Cannes. Two motions of no confidence were made by the right-wing opposition (the Northern League and the ex-Christian Democratic splinter groups CDU-CDR), against the Justice Minister, Giovanni Maria Flick, and the Interior Minister, Giorgio Napolitano, stating that Gelli had benefited from accomplices helping him in his escape. They also made reference to secret negotiations which would have allowed him to reappear without going to prison. But the two ministers won the confidence vote. Police found $2M worth of gold ingots in Gelli's villa.
A few years after the Ambrosiano scandal, many suspects pointed toward Gelli with reference to his possible involvement in the murder of the Milanese banker Roberto Calvi, also known as "God's banker", who had been jailed in the wake of the collapse of Banco Ambrosiano. On July 19, 2005 Gelli was formally indicted by Roman Magistrates for the murder of Roberto Calvi, along with former Mafia boss Giuseppe Calò (also known as "Pippo Calò"), businessmen Ernesto Diotallevi and Flavio Carboni, and the latter's girlfriend, Manuela Kleinszig. In his statement before the court Gelli blamed people connected with Calvi's work in financing the Polish Solidarity movement, allegedly on behalf of the Vatican. He was accused of having provoked Calvi's death in order to punish him for having embezzled money owed to him and the Mafia. The Mafia also wanted to prevent Calvi from revealing how the bank had been used for money laundering. Gelli's name, however, was not in the final indictment at the trial that started in October 2005, and the other accused were eventually acquitted due to "insufficient evidence", though by the time of these acquittals in June 2007, the prosecutor's office in Rome had opened a second investigation implicating Gelli, among others. In May 2009, the case against Gelli was dropped. According to the magistrate there was insufficient evidence to argue that Gelli had played a role in the planning and execution of the crime. Gelli has been implicated in Aldo Moro's murder, since the Italian chief of intelligence, accused of negligence, was a piduista (P2 member).
In 1996, Gelli was nominated as a candidate for the Nobel Prize in Literature, supported by Mother Teresa and Naguib Mahfouz. In 2003 Gelli told La Repubblica that it seemed that the P2 "democratic rebirth plan" was being implemented by Silvio Berlusconi:
Every morning I speak to my conscience and the dialogue calms me down. I look at the country, read the newspaper, and think:
"All is becoming a reality little by little, piece by piece. To be truthful, I should have had the copyright to it. Justice, TV, public order. I wrote about this thirty years ago... Berlusconi is an extraordinary man, a man of action. This is what Italy needs: not a man of words, but a man of action.
He talked of many Italian politicians. Of Fabrizio Cicchitto he said he knew him well (è bravo, preparato - "he's good and capable"). With regard to Berlusconi's program for the reform of the judicial system, he boasted that this had been an integral part of his original project. He also approved of Berlusconi's reorganization of TV networks.
On 15 December 2015 Gelli died in Arezzo, Tuscany, aged 96.