Marsaglia will replace Francesco Gaetano Caltagirone, who holds a stake of just under 10% stake in Generali according to the latest filings and fought a campaign against the reappointment of the company's chief executive in April.
Caltagirone's two remaining nominees on the Generali board did not support the appointment of Marsaglia, Generali said in a statement.
It also said that Luciano Cirina, a former Generali executive who was Caltagirone's candidate for the CEO's job, "did not meet the requirements for appointment" to the board.
Cirina missed out on the CEO role in April when shareholders supported Philippe Donnet for a new term.
Marsaglia, an Italian, has worked in banking for Rothschild, Barclays and Mediobanca. He is currently CEO of private equity firm Azzurra Capital.
(Writing by Keith Weir; Editing Gianluca Semeraro and Mark Potter)