A long-time Aung San Suu Kyi loyalist has vowed to prioritise the rule of law, peace and reconciliation after being sworn in as the country's new president.
Win Myint will continue his predecessor's deference to Ms Suu Kyi as the de facto national leader.
The 66-year-old, who is the former lower house speaker, took his oath of office during a joint session of parliament, pledging loyalty "to the people and the republic of the Union" of Burma.
First vice president Myint Swe, a military nominee and second vice president Henry Van Tio, an upper house parliament nominee, took oaths alongside him.
Ms Suu Kyi and powerful army chief Senior General Min Aung Hlaing watched the swearing-in.
For many years a political prisoner under the military that then ruled Burma, Ms Suu Kyi cannot become president because the junta-drafted 2008 constitution bars those with foreign family, which directly aimed to bar Ms Suu Kyi from becoming head of state. Her two sons are British.
Burma's military ruled with an iron fist before handing power to a civilian government led by Ms Suu Kyi in 2016.
The military still holds considerable power, with control of national security and other government functions and a quarter of the seats in Parliament.
Ms Suu Kyi said when her government took office that she would be "above the president". She led the government in that manner during the presidency of her close friend, Htin Kyaw, who retired last week because of ill health.
In his inaugural speech, Win Myint vowed to work on amending the constitution.
"As part of the priorities of the union government, amending the constitution is the most fundamental to build the federal democratic government," he said. "I will prioritise to implement the rule of law, for the improvement of people's life, national reconciliation and internal peace."
Burma's civilian government has come under international pressure for its handling of a crisis in northern Rakhine state, where security forces have been accused of ethnic cleansing and serious human rights violations that have caused about 700,000 Rohingya Muslims to flee to neighbouring Bangladesh.
"We are facing pressure, criticisms and misunderstandings at the international fronts and our country and our people are facing many challenges," Win Myint said in his speech. "Though everything will not be solved easily, I will try my best to solve the problems and prioritise them."