Néstor Guillén assumed office as the interim 40th President of Bolivia on 21 July 1946, and his mandate ended on 17 August 1946.

A magistrate of the Superior District Court of La Paz, Guillén was chosen to lead an interim junta in the absence of the President of the District Court Tomás Monje, who was ill at the time, in the wake of the violent demise of President Gualberto Villarroel.

[1] On 24 July 1946, the civil junta which made up Néstor Guillén's cabinet was expanded to include representatives from the labor, student, and magistrate sectors.

[4] Roberto Bilbao la Vieja, employed by the Asociacion de Industriales Mineros (Association of Mining Industrialists, a legal entity of the three tin magnates), was made Secretary-General.

Alcoba, Solares, and Bilbao la Vieja would remain in their positions until the end of Monje's mandate.