The writers say the violence sparked by the publication of cartoons satirising the Prophet Muhammad shows the need to fight for secular values and freedom.
The statement is published in Charlie Hebdo, one of several European papers to reprint the caricatures.
The images, first published in Denmark, have angered Muslims across the world.
One showed the Prophet Muhammad, whose depiction is banned in Islam, as a terrorist bomber.
Many newspapers defended their decision to reprint the cartoons on the grounds of freedom of expression.
Almost all of those who have signed the statement have experienced difficulties with Islamic militancy first-hand, says the BBC’s Caroline Wyatt in Paris.
They include Dutch MP and filmmaker Ayaan Hirsi Ali and exiled Bangladeshi writer Taslima Nasreen.
“After having overcome fascism, Nazism, and Stalinism, the world now faces a new global threat: Islamism,” the manifesto says.
“We, writers, journalists, intellectuals, call for resistance to religious totalitarianism and for the promotion of freedom, equal opportunity and secular values for all.”
The clashes over the cartoons “revealed the necessity of the struggle for these universal values,” the statement continues.
“It is not a clash of civilisations nor an antagonism of West and East that we are witnessing, but a global struggle that confronts democrats and theocrats.”
The writers said they refused to accept that Muslim men and women “should be deprived of their rights to equality, liberty or secularity in the name of respect for culture or tradition”.
They also said they would not give up their critical spirit out of fear of being accused of Islamophobia.
“Islamism is a reactionary ideology which kills equality, freedom and secularism wherever it is present,” the writers added, saying it is nurtured by fears and frustrations.
Salman Rushdie – Indian-born British writer with fatwa issued ordering his execution for The Satanic Verses
Ayaan Hirsi Ali – Somali-born Dutch MP
Taslima Nasreen – exiled Bangladeshi writer, with fatwa issued ordering her execution
Bernard-Henri Levy – French philosopher
Chahla Chafiq – Iranian writer exiled in France
Caroline Fourest – French writer
Irshad Manji – Ugandan refugee and writer living in Canada
Mehdi Mozaffari – Iranian academic exiled in Denmark
Maryam Namazie – Iranian writer living in Britain
Antoine Sfeir – director of French review examining Middle East
Ibn Warraq – US academic of Indian/Pakistani origin
Philippe Val – director of Charlie Hebdo
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