He is replacing Cardinal Mario Pompedda, 75, who presented his resignation to the Pope for reasons of age.
Bishop Vallini, 64, who has been raised to the dignity of archbishop, was born in Poli, Italy, in the Diocese of Tivoli, near Rome.
His current diocese of Albano includes the town of Castel Gandolfo, site of the papal summer residence.
The Apostolic Signature adjudicates, among other things, complaints of nullity and petitions for total reinstatement against sentences of the Roman Rota.
It also adjudicates administrative controversies referred to it by the pope or by dicasteries of the Roman Curia, as well as conflicts of competence between these dicasteries.