Castello Branco was a member of Petrobas's board until 2016 and has also held executive positions at Brazil's central bank and at miner Vale SA.
He will take over from Ivan Monteiro, who will remain CEO of the oil company until Castello Branco is officially appointed by Brazil's President-elect Jair Bolsonaro who takes office on Jan. 1.
Petrobras representatives did not immediately reply to a request for comment.
Right-wing Bolsonaro said this month that Monteiro was not expected to stay on as CEO under Brazil's new administration.
Guedes, a pro-business free marketeer, has said he favours the full privatization of Petrobras. But nationalistic retired army generals in Bolsonaro's campaign team see the company as a strategic asset that must stay in state hands.
Castello Branco, who studied post-doctorate economics at the University of Chicago, has wide experience in both the public and private sectors, according to Guedes' statement. (Reporting by Rodrigo Viga; Additional reporting by Anthony Boadle; Writing by Bruno Federowski in Brasilia; Editing by Susan Fenton)
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