He was 89.
His funeral and other ceremonies would be announced later, the National Commission of Health Services for Officials said.
Phieu, whose hometown is in north-central Thanh Hoa Province, served in several positions in the military between 1946 and 1992, rising to colonel general and head of the general political department of the People's Army.
He was elected to be a member of the Party Central Committee in 1991, before being elected into the Secretariat, which is in charge of the party's administration affairs, in June 1992.
He became a member of the Politburo, the Party's decision-making body, in January 1994.
In December 1997 he was elected general secretary of the Party, a position he held until April 2001.
He is remembered for a resolution that set out the mission to build the party into a force for fighting corruption.