Like China, Vietnam is ruled by a communist party but, unlike its neighbour, it has engaged in more collective decision-making with leaders being subject to multiple checks.

But if Lam, 67, were to continue to wear both the president and party chief hats, as Xi Jinping does, for some time, the Southeast Asian nation could see a more autocratic style of leadership, according to analysts, diplomats and activists.

Some investors would welcome the emergence of a stronger leader who could put an end to over a year of political wrangling, they said. The wrangling has had a negative impact on investment in a country that is home to large manufacturing operations for dozens of top multinationals.

Economic and foreign policy are not expected to change substantially, but civil liberties could be further eroded, they warned.

"If Lam became the most powerful man in Vietnam without checks and balances it would be bad for Vietnam and erode the norm of democratic centralism," said Carl Thayer, a senior expert on Vietnam at the Australian Defence Force Academy.

It is, however, not clear how and when the party would replace Trong with an acting general secretary or a permanent one.

Lam could, in theory, continue in both roles until 2026 when all top jobs will be up for grabs for the next five-year term. Trong himself held the two positions for nearly three years until April 2021 after the death of a former president.

But Lam may face internal opposition that could even lead to a succession crisis, said Le Hong Hiep and Nguyen Khac Giang from the Singapore-based think tank ISEAS–Yusof Ishak Institute in an article published on Friday.

STELLAR RISE

The son of a senior police officer, Lam studied security and obtained a PhD in law. He went on to become the minister for public security in 2016, a four-star general and was admitted in 2021 to the Communist Party's Politburo, the most powerful body in the country.

His ascent in roughly three months this year from minister to president and now also assuming the party chief's duties only underlines his grip on power, according to experts. His election as president had been seen as a "stepping stone" to the party chief job, they add.

Lam also appears to have maintained indirect control over the powerful public security ministry, which is now led by an official who hails from Lam's native province and is seen as close to him.

Lam's intense focus on public security is clearly outlined in his 2021 book titled "New Findings on National Security for the 13th Party Congress".

"The combination of national security together with economy, culture and foreign affairs is a must in our Party's vision in order to both build and protect socialism at the same time," he wrote.

He has been a central figure in the fight against corruption, Trong's signature policy known as "blazing furnace" that has been in place since 2017 and has recently intensified.

Since 2023, two of Vietnam's presidents and one chair of parliament have quit over unspecified wrongdoing, with the public security ministry playing a central role in the investigations.

Lam's access to intelligence and sensitive information has also meant that he is feared, with Western diplomats often lowering their voices or not naming him when referring to Lam in private meetings.

Last year, a noodle vendor was sentenced to five years in prison after posting a video that was considered to be mocking Lam. In the video, the vendor imitated a celebrity chef who fed Lam a gold-encrusted steak at his London restaurant while Vietnam was under COVID-19 lockdowns in 2021.