One week of commemoration activities will begin with Mr Kagame lighting the flame at the memorial, where some 250,000 victims are said to be buried.
The 61-year-old president, who has led the country since the end of the genocide, is scheduled to make a speech at the Kigali Convention Centre.
He will then lead a vigil at the Amahoro National Stadium, which was used by United Nations officials to try to protect Tutsis during the killings.
Who is attending?
A number of foreign leaders are expected to be at some of the events. They are mainly African, although Prime Minister Charles Michel will represent the former colonial ruler, Belgium.
France was a close ally of the Hutu-led government prior to the massacres and has been accused of ignoring warning signs and training the militias who carried out the attacks.
France will be represented by Herve Berville, a Rwandan-born MP.
Ugandan President Yoweri Museveni will also not be there. He has been accused of backing Rwandan rebels who oppose Mr Kigali.
How did the genocide unfold?
On 6 April 1994, a plane carrying then-President Juvenal Habyarimana – a Hutu – was shot down, killing all on board.