The amnesty deal with Catalan separatists has prompted a wave of protests across Spain.
Authorities said 80,000 people gathered in Madrid on Sunday, while tens of thousands also attended demonstrations in Granada and Seville.
Thousands have congregated each night for nearly a fortnight outside the Socialist Party (POSE) headquarters in Madrid.
"We are Spaniards worried about Spain," said one young protester draped in a Spanish flag.
The Supreme Court on Wednesday rejected an injunction by the far-right party Vox to suspend the investiture vote.
Persons:
Sanchez, Pedro Sanchez's, Junts, Vox, Adolf Hitler, Esteban Gonzalez Pons, Alberto Nunez Feijoo, Belen Carreno, Miguel Gutierrez, Charlie Devereux, Aislinn Laing, Emelia
Organizations:
Spain's, Amnesty, Spain MADRID, Police, ERC, Sanchez’s Socialists, People's Party, Authorities, Sunday, Socialist Party, Eastern, European, Sanchez's Socialist Party, PSOE, Junts, Thomson
Locations:
Spain, Spain's, Madrid, Catalan, Granada, Seville, Spanish, Hungary, Romania