Monroy was murdered during a meeting in the Pereira department. After fighting in the Revolutionary Armed Forces of Colombia-People's Army (FARC-EP) militias, she was undergoing her reincorporation process.
INDEPAZ also reported the murder of Maria Lopez Cordon, who was a social leader in the Caño Lindo municipality in the Meta department.
Last week, the Special Jurisdiction for Peace (JEP) revealed that 283 former FARC-EP members had been killed in Colombia from 2017 to date.
Lawmakers from the Revolutionary Alternative Force of the Common party (Comunes) and feminist activists expressed their rejection of Monroy's murder while demanding an investigation.
"We reject the assassination of Peace signer Blanca Rosa Monroy. We accompany her family and friends in their pain. Stop the genocide! Not one less! We want Peace!." Senator Sandra Ramirez said.
INDEPAZ highlighted that at least 36 former combatants have been killed so far this year.
#Colombia | The Red Cross on Sunday expressed concern for at least 2,600 people facing displacement in the town of Santa Rosa in the Risaralda department, calling on armed groups to respect humanitarian norms. pic.twitter.com/sh20eEn4Zf