Venner, a longstanding far-right theorist, left a suicide note on the altar before blowing his brains out in front of 1,500 visitors on Tuesday afternoon.
In a message read out on a right-wing radio station, Radio Courtoisie, after his death he declared, "I am killing myself to awaken slumbering consciences."
And in a final blog he called the marriage reform a “vile law” and called on its opponents it to tackle the “peril” of a “great replacement of the population of France and Europe” and warned against France “falling under the power of Islamists”.
But the best-known leader of the protests against the gay marriage law, Frigide Barjot, on Wednesday declared that the suicide had “nothing to do” with the demonstrations and was “an isolated personal act”.
Venner belonged to the Printemps Français (French Spring) movement, “which we condemned a very long time ago”, Barjot told a press conference, adding that she has received numerous death threats from far-right supporters and calling on Interior Minister Manuel Valls to provide tighter security for her.
Mainstream right-wing MP Hervé Mariton, who has vociferously opposed the law, was more ambiguous in his response.
“I’m saying that a man is dead and I respect him,” Mariton told BFMTV.
He did not agree with everything Venner stood for, Mariton said, but “there are some points that I can agree with”.
Far-right Front National leader Marine Le Pen was forced to partially retract her fist tribute to Venner, who had considerable influence on many of her followers.
In a tweet she hailed an “eminently political act” aiming “to wake up the people of France” but a second corrected the apparent endorsement of suicide by declaring "it is in life and hope that France will renew and save itself".
With another demonstration against the “marriage for all” law scheduled for Sunday, Socialist MP Christophe Cambadélis dubbed the suicide “a call for sacrifice”, which would “excite a little more those young people who are becoming radicalised” and slammed the right-wing UMP party for supporting the protest.
Dominique Venner, 78, was a longstanding far-right activist and essayist.
In 1954 he set up a nationalist group called Jeune Nation (Young Nation), which opposed France leaving Algeria and was banned in 1958.
Its members went on to join the Organisation Armée Secrète (OAS), which carried out armed attacks, including the attempted assassination of President Charles De Gaulle, in support of France’s continued colonial rule in Algeria.
Venner was jailed and, on leaving prison in 1963, set up Europe-Action, a movement that influenced the violent far-right student group, Occident, to which Sarkozy-era defence minister Gérard Longuet and several other well-known politicians belonged.
His writings are credited with reorientating the far right in the post-colonial era, stressing European identityand focussing on a perceived cultural threat to the West posed by immigration.
Criticising Christianity for being a “universalist” religion, he became a practicing pagan, seeking the religion “at the sources of European identity” before the Judaeo-Christian era.
In his book Le Choc de l'histoire (The Shock of history) he praised the suicide of Japanese writer Yukio Mishima in 1970, describing it as a “protest against the idignity into which his country had fallen”.
Mishima, a fellow far-right nationalist, was gay.