The Catholic charity said Iván Duque Márquez's first official visit to the UK since he was elected last year is a chance to "save the peace deal" with the country's largest guerrilla group, the Revolutionary Armed Forces of Colombia (FARC).
Ulrike Beck, CAFOD's Colombia Programme Officer, said: "This is a crucial time to address the challenges and rescue the deal.
"When Ivan Duque became president of Colombia last year, the future of the country seemed bright - after five decades of internal armed conflict, a peace agreement was reached in 2016, and although fragile, peace seemed possible."
However, negotiations with the South American country's second largest guerrilla group - The National Liberation Army (ELN) - have broken down, shattering hopes of a peace deal with FARC.
Beck added: "The UK has a key role in supporting the peace process, being the pen-holder for the UN resolutions establishing the UN missions to monitor its implementation.
"Over the last year, the humanitarian situation has got worse for people living in rural areas and threats and killings targeting rural community leaders and human rights defenders have increased.
"Since the signing of the peace agreement more than 400 community leaders and other human rights defenders have been killed, many of them local leaders who were key for the implementation of the agreement.
"The UK is Colombia's second biggest foreign investor, behind the US. In a post-Brexit scenario and given the ongoing armed conflict in the country, trade deals and investment in Colombia should not benefit from any human rights abuses that have or are currently taking place."
Colombia's negotiated peace agreement with FARC - which won former Colombian President Juan Manuel Santos the 2016 Nobel Peace Prize - ended the longest-running armed conflict in the Western Hemisphere.
Fighting killed 200,000 people and displaced a further 7 million people between 1964 and 2016.
Despite the deal - which included offering reparations to war victims - being rejected in a referendum, Congress passed it in November 2016.
The peace deal is yet to be agreed upon and remains controversial.
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