Petroni was a leader of the Morenoist tendency of Latin American Trotskyism from 1973 to 1988 and was a close collaborator of the founder of this movement, Nahuel Moreno. Petroni has contributed to, edited or published more than 30 political newspapers, magazines and websites around the world and is the author of half a dozen books on politics, Marxist theory and political organizing. He is also known at times by some of his pen names: Leon Perez, Nicholas Kramer, and Simon Morales.
Petroni was a founder of and/or leading participant in numerous Trotskyist groups in Latin America, Europe and the United States, he has extensive organizing skills and experience in working class struggles. Petroni was a member and leader of the Argentine Partido Socialista de los Trabajadores (PST) from 1973 to 1976, and during the beginning of the military dictatorship was part of its underground continuation. As an elected leader of unions representing printers, metal workers, meatpackers, social workers and others, he led strikes, organized unions and support, ran for public office and was involved in various working class struggles for almost four decades.
As a result of his trade union and political work in Argentina, he was the target of three assassination attempts during 1974 and 1975 by death squads organized by the Argentine Anticommunist Alliance (Triple A). The Triple A operated under the protection and support of Peronist governments from 1973-1976. Many members of the Triple A collaborated with the military dictatorship after 1976.
Petroni went into exile in 1978. From 1978 to 1985 he was responsible for the North, Caribbean and Central American Secretariat of the Morenoist tendency.
He participated in the Nicaraguan and Salvadoran Revolutions in the late 70s, helped found the Nicaraguan section of the IWL, helped develop other Central American organizations and the Mexican section of the Morenoists. He was a delegate and member of the Presidium of the Morenoist international tendency in its different stages: Bolshevik Tendency of the Fourth International (1976–1980), International Committee of the Fourth International (1981) and International Workers League (Fourth International)—Liga Internacional de los Trabajadores (Cuarta Internacional or LIT(CI)) from 1981 to 1988. After the collapse of the military dictatorship he travelled extensively around the Americas and Europe then became a leader of the Movement for Socialism (Argentina), from 1985-1988.
Prior to that he (as well as Nahuel Moreno) worked as a member of the International Committee of the LIT(CI) and its International Secretariat from 1982 until the death of Moreno in 1986. He was also a founding member of its US section, eventually called the Internationalist Workers Party (IWP). He was expelled from the LIT(CI) in 1988, as was the IWP, after Nahuel Moreno's death, and Petroni then continued his political work in the USA. In the late 1990s he became a member of the Committee for a Workers' International (CWI) and its affiliate in the USA, Socialist Alternative (US), and after leaving the CWI in 2002, he helped found a group called the Left Party in the USA.
Petroni was very active in the San Francisco elections. For example, he ran for the Board of Supervisors in 1998 obtaining 16,293 votes (2%). The next election he ran for City Treasurer and obteined less votes, 14,911, but it reached 13% of the votes given the very low turnout, against the winner with 87% and 99,408 votes. In 2000, he wrote and managed Proposition F, considered a historical reparation Act for African American City residents, which obtained more than 45% of the vote. He ran for different offices from the mid-1990s until he returned to Argentina after the 2004 election. He also supported, organized and managed other campaigns and significant local ballot initiatives.
As of 2006, he is back in his native Argentina where he is editing the online and print versions of Izquierda.info. Petroni has also emerged as an official witness in the trial for "crimes against humanity" attributed to members of the Triple A. Petroni has introduced into the federal court proceedings motions asking Judge Oyarbide to order the arrest of more than a dozen members, mostly union officials from Mar de Plata, Argentina, of the right wing terrorist organization CNU (which became part of the Triple A) and to question in court the knowledge of their crimes by their associate and present day General Secretary of the CGT, Hugo Moyano, who is now also vice president of the Peronist Justicialist Party.
Petroni currently resides with his son in Buenos Aires.