Born in 1968 at Hyesan, Park grew up in a privileged family in North Korea. After graduating college, he was given a job at the government propaganda office in Pyongyang. He met with other members of the community every Sunday to engage in “self-judgment.”
Park worked at the propaganda office until 1999. In that year, his father "decided he had had enough". During the late 1990s many top intelligence officers had been purged, and Park's father, who at the time was posing as a businessman in Hong Kong, feared the regime would have him killed if he returned to North Korea. He sent a message to his family through a broker, ordering them to flee to China.
After bribing North Korean guards to look the other way, Park and his brother swam across a river into China, while their mother and sister floated across the river using an inner tube. They were picked up on the other side of the border by a car, as arranged by his father, and the whole family flew on false passports to South Korea.
Following the family's escape, an uncle of Park's in North Korea was beaten to death in retaliation for their defection.
In 2006, Park became the chairman of the Democracy Network against North Korea Gulag. As of 2013, he is the chairman of Fighters for a Free North Korea.
In April 2015 Park Sang-hak was detained as protestors clashed with South Korean police over their attempts to airlift thousands of copies of The Interview into North Korea.
Fighters for a Free North Korea is known for periodically launching balloons carrying human rights and pro-democracy literature, DVDs, transistor radios and USB flash drives from South Korea into North Korea. Over two million such balloons have been launched. The balloons, which generally reach the Pyongyang area after three to four hours in the air, are timed to release their materials in the Pyongyang area.
According to the Wall Street Journal, supporters of the balloon campaign say that it "is one of the most effective tools for change inside North Korea, where information about the outside world is highly restricted". Critics of the campaign, reported the Journal, "oppose the move for causing inter-Korean frictions".
Park and his colleagues released balloons containing leaflets from Ganghwa, an island off the west coast of South Korea, in October 2012, shortly after being prevented by authorities from releasing them from Paju, their usual launch site, which North Korea had threatened to fire upon if the balloon release went forward.
In September 2011, a North Korean defector was arrested in Seoul by members of the National Intelligence Service on his way to meet with Park, referred to as "Enemy Zero" by the Pyongyang regime. South Korean authorities said that he had planned to kill Park either by poisoning his drink or by jabbing him with a poisoned needle. Park said that the assassin, Ahn, had phoned him earlier and asked to meet him. "Ahn told me by phone", Park said, "that he was to be accompanied by a visitor from Japan who wants to help our efforts. But then I was told by the NIS not to go to the meeting due to the risk of assassination".
The Independent of London noted that Ahn "could face the death penalty" under South Korea's National Security Law, but he ended up being sentenced to four years in prison. He was also ordered to pay 11.75 million Won in fines (about $10,000 USD ), which was the same amount he had been promised for assassinating Park. The Independent also pointed out that the assassination plot was “reminiscent of the Cold War killing of Bulgarian dissident Georgi Markov, who was stabbed with a ricin-tipped umbrella in London in 1978.”
In May 2013, Park was presented with the Václav Havel Prize for Creative Dissent by the Human Rights Foundation.