He was the son of José Santiago Gandarillas Guzmán and María del Carmen Luco Huici.

His uncle was Senator Manuel José Gandarillas Guzmán, who served as Ministry of Government and Foreign Affairs under Ramón Freire, the first President of Chile.

[4] Under the Aníbal Pinto, a Liberal and the 8th President of Chile, Gandarillas served as the Minister of Justice, Worship and Public Instruction.

During this period, he was a member of the permanent commissions of Government and Foreign Relations; Constitution, Legislation and Justice; Finance and Industries and Worship and Colonization.

[3] Gandarillas was married to Rosa Huici Arguedas, one of thirteen children born to Ildefonso Huici y Peón, a silver magnate who had fled civil war and moved his family to their estates in La Calera, Chile, then a village in the banks of the Aconcagua river, some sixty kilometers (about forty miles) northeast of Valparaíso.