Manuel Rocha was charged with secretly passing information to the Cuban government since 1981.
A former career US diplomat who had served as the US ambassador to Bolivia has pleaded guilty to working as an agent of Cuba for more than 40 years.
Victor Manuel Rocha, 73, was charged with secretly passing information to the communist-run Cuban government since 1981 while working for the US state department.
On Thursday, he changed his initial not guilty plea in a court in Miami.
He is due to be sentenced at a hearing on 12 April.
The move brings one of the highest profile espionage cases between Cuba and the US to an unexpectedly rapid conclusion.
International policies, USA agents infiltrated in other governments and agencies, policy road maps and how to sabotage them.
Without getting out of my depth the possibilities to create mayhem and fend off any effort, good or bad.
Go read a John le Carre book to understand what spies can do and don't.