Petro made the call on Twitter after a video appeared in which the controversial former president was repeatedly called a “murderer” during a visit to a university.
The leftist politician urged Colombians to come together amid a highly polarized election campaign that saw Petro physically attacked in March.
“I call on citizens to respect ex-President Alvaro Uribe. Whatever the differences, whatever the judicial decisions may be, we’re talking about the representative of part of our society. It’s time to understand each other, to live together. It’s time for one Nation,” Petro tweeted.
Petro’s words come just days after the remaining presidential candidates signed a non-violence pact, agreeing to put an end to the “intolerance” and “physical aggression” seen in an electoral campaign blanketed by intimidation and persecution.
Uribe and Petro have been bitter rivals since 2004 when the former guerrilla exposed extensive ties between the country’s ruling elites and far-right death squads.
Petro’s accusations triggered the arrest of more than 60 congressmen, including the cousin of the former president.
Colombia’s Supreme Court opened an investigation into Uribe a month before legislative elections in March.
The former president is suspected of intimidating witnesses who claim Uribe was a leading force behind the formation of a death squad in his home province of Antioquia.
The Supreme Court investigation fueled animosity between left and right that had already led to several clashes during the first election campaign since the demobilization of Marxist FARC guerrillas.
In March, Petro and FARC candidate Rodrigo Londoño were physically attacked after incitement by political rivals.