In an interview with Voice of America's Persian Service, Heydari urged other Iranian diplomats to do the same.
"They should resign to support the Iranian people," he said. "Our priority should be the best interests of the people, not our own personal interests."
Heydari said what pushed him to resign was the government response to demonstrations on Ashura, a holy day for Shiite Muslims. He described the government reaction as "force and brutality."
Last year's presidential election has been followed by large street protests. The official results were a landslide for President Mahmoud Ahmadinejad but there were major indications of fraud, including the president's strong showing in the home regions of his major opponents.
"When I watched what has been happening in Iran … I thought, 'I want to join the people of my country, and tell them, inside and outside Iran, that I support them and I am hoping for the same changes they are,'" Heydari said.
The consul quit his post in Oslo late last week. His interview with VOA was his first effort to reach Iranians.