Director of the General Department of Politics Luong Cuong has been assigned by the Politburo to replace her.
Mai, 66, was first assigned by the Politburo to be the Permanent Member of the Secretariat over a year ago. She has been a member of the Politburo, the Central Party Committee and a National Assembly delegate.
Cuong, 67, has been a member of the Central Party Committee, the Politburo and the Secretary of the Central Party Committee. He enrolled in the army in 1975, before becoming Vice Director of the General Department of Politics in 2011. He became director in 2016.
The Central Party Committee said Mai was entrusted with many important leadership positions of the Party and the state. She has demonstrated high responsibility and fulfilled her missions well, making important contributions to the Party's leadership and the National Assembly's operation.
However, she had committed violations to Party regulations, according to reports by the Central Inspection Commission, it said, adding these violations have negatively affected the reputation of the Party and herself.
Mai has asked to leave all her positions and retire, it said.
The Central Secretariat Committee is the highest implementation body of the Party, implementing the decisions of the Politburo and the Central Committee.
Mai stepping down has been the third major change in Vietnam's leadership in less than two months.
On March 20, the Central Party Committee granted Vo Van Thuong's resignation as president. The National Assembly officially voted for him to step down the next day and for Vo Thi Anh Xuan, previously vice president, to be acting president.
On May 2, the National Assembly granted Vuong Dinh Hue's personal request to step down as its chairman, after the Central Party Committee approved his resignation.