Olivares, an elected lawmaker for La Rioja Province, died Sunday, three days after being seriously wounded in a gun attack that also killed provincial official Miguel Marcelo Yadón.
Olivares, 61, and Yadón, 58, were shot at least six times last week just outside the National Congress building in what Security Ministry officials described as a "mafia-style" attack.
Macri and politicians from rival parties put their differences behind to attend Monday's wake at the lower house of Congress in Buenos Aires. Olivares' coffin was displayed at the Salón de Pasos Perdidos, where lawmakers could pay tribute to their fallen colleague.
"This is a great sadness, it is inexplicable. Olivares will be remembered as a great person, I can not comment on what justice is investigating, but I ask them to get to the bottom of it," said pro-government deputy Daniel Lipovetzky at a press conference.
At least six people have been detained through the investigation into the attack, including two who are believed to have carried out the attack. Investigators believe the attack was of a personal nature and aimed primarily at Yadón.
Security Minister Patricia Bullrich said this week the attack was carried out by "a whole clan of gypsies."