Spain's Attorney General (AG), Jose Manuel Maza, died unexpectedly while attending a conference in Argentina on Saturday.
The news was confirmed, on social media, by Spanish Prime Minister Mariano Rajoy, who expressed condolences for Maza's family.
According to a BBC report, Maza was admitted to hospital for a kidney infection. The prosecutor had only been in the position for less than a year. He was leading the investigation against the 14 recently deposed members of Catalonia's dissolved government.
Justice Minister Rafael Catalá described Maza as an extraordinary lawyer and public servant.
The Spanish government will be required to select a candidate to fill Maza's role following a hearing of the General Council of the Judiciary.
That candidate of choice must then be approved by a Congress commission and the king.
Ousted Catalan leader, Carles Puigdemont, is contesting extradition from Belgium.