Lam took over the duties of party chief on July 18, replacing Nguyen Phu Trong the day before his death as his health deteriorated.
Party delegates unanimously supported Lam's nomination, officials told a press conference on Saturday.
Addressing the delegates, Lam vowed to inherit and promote Trong's legacy, make no changes to the Southeast Asian nation's foreign policy, focus on achieving its socio-economic development goals and "fiercely" continue Vietnam's anti-graft campaign.
Former Communist Party leader Nguyen Phu Trong died on July 19 after a 13-year reign. (AP PHOTO)
"In the coming time, the work on anti-corruption will be continued fiercely," Lam told reporters.
"I feel fortunate that I have much experience in handling anti-graft campaign during the time I worked at the police ministry."
Vietnam, a major destination for manufacturing investment, has long been favoured by multinational corporations for political stability but in recent months has experienced major political turbulence officials said was fuelled by the anti-corruption campaign.
Vietnam does not formally have a paramount leader, but the head of the party effectively plays a more prominent role than others after Trong strengthened the powers of the role during his 13-year tenure.
Lam, a career security officer, had been seen as long aiming to become party chief, with experts calling the presidency a stepping stone for the top job.
It was not immediately clear whether Lam would keep both top jobs until the end of this legislative session in 2026, or whether a new president would be chosen.
Lam was elected president in May after leading a sweeping campaign of high-profile investigations against corruption as police minister.
He replaced Vo Van Thuong, who had been in the job about a year when he quit amid accusations of unspecified wrongdoing.
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