Pierre Laval is another notable example.
He didn't come exactly from far-left, but is of course a big example.
Of course, Doriot.
Paul Marion, who was a small French Goebbels and may qualify for the word "populist" !
Henri Barbé et Pierre Célor, from the famous Barbé-Célor purge.
René Belin was from the CGT, even if a non-communist wing.
Marcel Déat was a socialist, Charles Spinasse also.
Drieu la Rochelle in a way.
Gaston Bergery was a radical.
Bertrand de Jouvenel and... René Bousquet were from the centre-left.
Camille Chautemps wasn't from the right originally.
Oh, I'm a bit far away from your question, but, anyway, this
dérive fasciste was widepsread !
You can add some former Soviet communists who are now the biggest nationalists in Russia.
And Meciar wasn't a communist for a long time when he reached prominence after 1989, but, well, he was one in the beginning. And he is a REAL populist !