Giulio Tremonti told the ANSA news agency that he was also suing Alessandro Sallustri, editor-in-chief of Il Giornale daily that printed tweets by 30-year-old journalist Francesca Immacolata Chaouqui.
Chaouqui was last month named the only female and only Italian on a panel to review the Vatican's financial administration.
"Having nothing to do at all with two well known Vatican 'lobbies', I am taking legal action against Chaouqui," Tremonti said.
Chaouqui reportedly made a number of controversial posts on Twitter before her appointment, including one in March when she called Vatican secretary of state Cardinal Tarcisio Bertone "corrupt".
She alleged the Vatical official had shady business links to an unspecified Italian company.
One of Chaouqui's tweets read: "Tremonti held an account with the Vatican Bank. They shut it down when they found out he's gay."
Another of her tweets in February stoked rumours that former pope Benedict XVI had cancer. Benedict abdicated in February citing old age and frailty.
Chaouqui's Twitter account has since been shut down. She claims the messages were tweeted by other people who had access to her account.