Speaking on the first day of a party conference, Raul Castro said his resignation will allow a younger group of politicians "full of passion and anti-imperialist spirit" to take control.
"I believe fervently in the strength and exemplary nature and comprehension of my compatriots, and as long as I live, I will be ready with my foot in the stirrups to defend the fatherland, the revolution and socialism," he said at a closed-door meeting, according to NBC News.
Raul Castro has served as first secretary of the Communist Party of Cuba since April 2011, when he took over for his brother, who held the position for more than 45 years. Raul Castro also served as president of the country from 2008 to 2018, and acting president during the last two years of Fidel Castro's tenure.
Fidel Castrol died in 2016 after decades of power in the Caribbean island nation.
Current President Miguel Díaz-Canel is expected to take over leadership of the Communist Party with Raul Castro's departure.
NPR reported that Raul Castro's long-time deputy, José Ramón Machado, also was expected to step down in his role of the Politburo, leaving the body without any revolutionary veterans for the first time in decades.