In 1976, Park was charged with bribing members of the U.S. Congress, using money from the South Korea government, in an unsuccessful effort to convince the United States government to keep troops in Vietnam. In 1977 he was indicted by a U.S. District Court on 36 counts, including bribery, illegal campaign contributions, mail fraud, racketeering, and failure to register as an agent of the Korean Central Intelligence Agency. He avoided a federal trial by testifying to the court in exchange for immunity. His testimony did not have a major impact, though it led to three members of Congress getting reprimanded, and may have convinced Speaker of the House Carl Albert to not run for re-election.
In the early 1990's Park owned a members-only club/restaurant called "The Historic Georgetown Club" in Washington, D.C.
In 1992, he was approached by Samir Vincent, an Iraqi-born American who was lobbying unofficially on behalf of the Saddam Hussein regime, to try to create a program that would bypass the United Nations-approved economic sanctions of Iraq that had started in 1991. Park agreed, requesting a payment of US$10 million for his effort, which Vincent agreed to. Park served as a liaison between Vincent and then-United Nations Secretary-General Boutros Boutros-Ghali, whom Park was friendly with. In late 1996, partly as a result of Park's lobbying efforts, the U.N. Oil-for-Food Program began. After 1997, when Kofi Annan became the new secretary-general, the government of Iraq dropped its ties with Park; Park had received about US$2 million from them by then.
In 2005, Park's name surfaced as part of investigations into the oil-for-food scandal. In July 2006, he was convicted, in a U.S. federal court, on conspiracy charges. He became the first person convicted through the oil-for-food investigation.
On February 22, 2007 he was sentenced to five years in prison. He was also fined $15,000 and required to forfeit $1,200,000.