Organisers said that about 90,000 people had attended the rally, including politicians from a number of countries.
They sang and chanted slogans, waving yellow flags and banners reading: "In support of the Iranian people."
'End to democracy'
The group does not support any of the defeated candidates in the presidential election, who have complained that there were widespread irregularities.
However, organisers said that they wanted to express their support for the protesters who have staged a number of mass demonstrations in Tehran since the June 12 poll.
The rally in Paris took place as Iranian police and pro-government militias used tear gas, water cannon and batons to disperse protesters who had gathered in defiance of a government ban and warnings by the police.
Alireza Jafarzadeh, one of the organisers of the French rally, said that the people gathered in Paris "want an end to the clerical dictatorship in Iran and they want a secular democracy which is represented by Mrs Maryam Rajavi".
Many people in the crowd wore yellow vests reading "Viva Ashraf" or "Our Choice: Maryam Rajavi".
The organisation includes the People's Mujahidin of Iran or Mujahedeen-e-Khalq (MEK), which is considered to be a "terrorist" organisation by the United States.
MEK took part in the Islamic revolution in 1979 that brought Khomeini to power, but their ideology, a blend of Marxism and Islamism, put it at odds with the revolutionary government.
The group was driven from its bases on the Iran-Iraq border in 1981 and resettled in Paris.
It has previously targeted Iranian government officials and government facilities in Iran and abroad, but the group's supporters say it is no longer involved in violence.
The European Union recently removed the group from its list of banned "terrorist" organisations.
The NCRI has thousands of followers in Europe and the United States, but many analysts say its support in Iran is limited because of its collaboration with Iraq during the 1980-88 Iran-Iraq war.