The demonstration comes just months before France elects a new president, with rightwing Francois Fillon -- who says he is "personally" opposed to abortion but won't seek to make it illegal -- tipped to win.
Protesters waving signs that said "Protecting the weak is truly strong" were among more than 50,000 demonstrators in the French capital, organisers said.
President of the pro-life Jerome Lejeune Foundation, Jean Marie Le Mene, called on presidential candidates to set "public health policy that fights against abortion".
He condemned "legislation that has made abortion commonplace", especially a proposal before French parliament to extend to cyberspace a 1993 law criminalising "interference" in abortions in the form of "false information".
The original intent of the law was to prevent pro-life activists from physically blocking access to abortion clinics.
Rightwing politician Philippe de Villiers, without using Fillon's name, pointed to what he called a "totally hypocritical" attitude to abortion in an election year.
"Some politicians dip a hand into the holy water and suddenly say abortion is unacceptable," he said.
Each year, France records around 220,000 abortions, which have been legal since 1975. It is estimated that around one Frenchwoman in three undergoes the procedure in her lifetime.
Fillon is a devout Catholic who opposed a 2013 gay marriage bill that brought hundreds of thousands of people onto the streets in protest. He now wants to amend the legislation to partly repeal gay adoption rights.
Polls currently show far-right National Front head Marine Le Pen qualifying for the second round of France's presidential election in May where she is forecast to face -- and lose to -- Fillon.