The 30-year-old secured Hungary's fourth gold of the Games with a throw of 80.59 metres to finish ahead of defending champion Primoz Kozmus of Slovenia, who took the silver with his season's best effort of 79.36 metres.
Japan's Koji Murofushi, the 2004 Olympic champion and reigning world champion, took the bronze medal, also heaving a season's best of 78.71 metres. Another former champion, Szymon Ziolkowski of Poland, the 2000 Sydney Olympic gold medallist, finished seventh.
Pars, maintained Hungary's tradition in the event with their fifth gold, after finishing fourth in Beijing four years ago.
He took the lead with his first round throw of 79.14 metres and improved that two rounds later with the only throw over 80 metres in the competition.
"I just wanted to win it," he told reporters. "I wasn't thinking about anything else. From the first round it was obvious my competitors were not going to throw over 80 metres so I am happy with what I did."
The competition was held up for 15 minutes after a foul throw from Kozmus partly dismantled the cage which had to be re-assembled by officials, much to the good-natured amusement of the crowd at the Olympic Stadium.
- Koji Murofushi