More than 50 years since the last American soldier left Vietnam, Biden travelled to Hanoi to sign the agreement that will bring the former foes closer than ever before.
The Comprehensive Strategic Partnership with Vietnam is a major relationship upgrade for the US. It is the culmination of a relentless push by Washington over the past two years to strengthen ties with Vietnam, which it sees as key to counter China's influence in Asia.
It is also no small feat. The partnership with Washington is the highest level of diplomatic ties extended by Vietnam, one of China's oldest and staunchest friends.
Biden told reporters in Hanoi that American actions were not about containing or isolating China, but about maintaining stability in accordance with international rules.
"I think we think too much in terms of Cold War terms. It's not about that. It's about generating economic growth and stability," Biden told reporters in Hanoi on Sunday, in response to a question from the BBC.
"I want to see China to succeed economically, but I want to see them succeed by the rules," he said.
Signs of improved ties had already irked Beijing, which called them more evidence of America's "cold-war mentality".
But Hanoi has thought this through, said Le Hong Hien from Singapore's ISEAS-Yusof Ishak Institute, adding that the agreement with the US was "symbolic rather than [one of] substance".