Leftist Francia Márquez is running alongside former guerrilla Gustavo Petro, the favourite in polls, while Luis Gilberto Murillo would become vice-president if centrist Sergio Fajardo were to win.
Both are environmental activists and represent the poorest, most remote and neglected Colombian regions wracked by violence.
Some 9.3 percent of Colombia's population of 50 million identifies as black.
"Thank you, Gustavo Petro, for handing me this responsibility, which I know is great, in the name of women, in the name of the nobodies," Márquez said during her presentation on Wednesday at a hotel in Bogotá.
If elected, she said she would work to improve the lives of women, black and Indigenous people, peasants, the gay community and young people who led mass protests against President Iván Duque's government last year.
Lawyer Márquez, 40, finished second behind Petro in the left-wing presidential primaries on March 13 to decide who would lead the Historic Pact leftist alliance in the May 29 election.
The left wing made historic advances in those primaries, which also served as parliamentary elections, in a country that has only had right-wing governments.
Petro said Márquez would also head the equality ministry if he wins.
"From slavery to power... from exclusion to democracy, from permanent violence to peace," said Petro, 61.
Márquez survived an armed attack in 2019 when she was targeted for her defence of water resources in black communities.
The year before that she was awarded the Goldman Prize for her work defending the environment in the southwestern Cauca department where she was born.
Murillo, 55, is a mining engineer who studied in Moscow and is also a former environment minister and governor of the western Choco department, the poorest in the country.
"I want to be vice-president of the regions, of the people with no voice, the people that want to see themselves reflected and interpreted in the national government, because there is no other way to progress on the path to peace," said Murillo in an interview.
Fajardo won the centrist primary and will challenge Petro and the right-wing candidate Federico Gutiérrez, who has yet to name his running mate, in the election.