She is making the official visit to the African country at the request of Britain's Foreign Office.
The palace said the countess's visit will focus on addressing the devastating impact of sexual and gender-based violence in conflict, while supporting and empowering survivors and tackling the stigma they face.
She is being accompanied by Lord Ahmad of Wimbledon, UK Prime Minister Liz Truss's special representative on preventing sexual violence in conflict.
Security will be tight for the visit, which had been planned for months before the death of the queen.
In its recent history, the DRC has endured years of civil conflict in what has been called Africa's world war, with the loss of up to six million lives through fighting or disease and malnutrition.
A peace agreement was signed in 2002 but violence continued in some areas, requiring a large UN military force to try to maintain order.
This August, Africa's second-largest country faced rising regional tensions in the east, with weeks of deadly protests against UN peacekeepers.
The countess's visit is taking place in the run-up to the International Preventing Sexual Violence in Conflict Initiative Conference in London next month, which is being hosted by the UK government and which she will attend.
The countess publicly committed herself in 2019 to supporting the UK's work in helping victims of rape, sexual violence and exploitation in war.
Last year she said that hearing survivors' stories of sexual violence took her to “some very dark places” during her work to raise awareness.
“Every story I am told is pushing me forward. I feel obligated to tell people this is happening — it is their story to tell and I support them,” she said.