[2][3] Croissier, who went on to Paris to further continue post-graduate studies in Economics, returned to Spain in 1974 and joined the Spanish Socialist Workers' Party (PSOE).

[3] Croissier, who had run as candidate in the PSOE list vis-à-vis the 1982 general election, became a member of the Congress of Deputies in 1983, covering the vacant seat for Madrid left in the lower house by Francisco Fernández Ordóñez.

[5] Considered to be close to Carlos Solchaga,[6] Croissier became the President of the Instituto Nacional de Industria (INI) in 1984.

[2] Appointed as Minister of Industry and Energy of the second González cabinet, he was sworn in in July 1986, at 35 years old.[1][n.

[8] He has been a member of the board of directors of companies such as Adolfo Domínguez, Eolia, High Tech Hoteles, Jazztel, Repsol YPF and Alantra.