The 81-year-old Castro also said he hopes to establish two-term limits and age caps for political offices including the presidency — an astonishing prospect for a nation led by Castro or his older brother Fidel since the 1959 revolution.
The 52-year-old Diaz-Canel is now a heartbeat from the presidency and has risen higher than any other Cuban official who didn't directly participate in the heady days of the revolution.
"This will be my last term," Castro said, his voice firm.
In his 35-minute speech, Castro hinted at other changes to the constitution, some so dramatic that they will have to be ratified by the Cuban people in a referendum. Still, he scotched any idea that the country would soon abandon socialism, saying he had not assumed the presidency in order to destroy Cuba's system.
"I was not chosen to be president to restore capitalism to Cuba," he said. "I was elected to defend, maintain and continue to perfect socialism, not destroy it."