Zaroubejneft did not immediately respond to AFP's requests for comment on the list posted to the e-disclosure.ru website run by the Interfax news agency, which said Fillon had been on the board since June 28.
Fillon, who ran the French government under President Nicolas Sarkozy between 2007 and 2012, works for the state-owned fossil fuels company in his role as head of Apteras, a consultancy he set up after an ignominious 2017 presidential bid.
His campaign was capsized by a fake-jobs scandal, for which a court sentenced him in June 2020 to five years in prison, three suspended.
He has already worked with Russian firms through Apteras and was nominated for his role on the Zaroubejneft board by the government in Moscow in early June.
Fillon is just the latest in a string of former senior European politicians to join Russian fossil fuel companies.
Austrian ex-foreign minister Karin Kneissl, who notoriously danced with President Vladimir Putin at her wedding in 2018, was in June named to the board of oil giant Rosneft.
Former German chancellor Gerhard Schroeder has been chairman of the Rosneft board since 2017, earning $600,000 a year.
