The 66-year-old, in the capital Naypyidaw for the ceremony, stood to read the brief oath in unison with 33 other members of her National League for Democracy party elected to the lower house in April.
The oath hands Suu Kyi public office for the first time and marks a transformation in the fortunes of the opposition leader, who was held under house arrest for much of the last 20 years but is now central to the nation's tentative transition to democracy.
Suu Kyi had initially baulked at taking the oath, specifically a sentence pledging to "safeguard" the army-created constitution.
But on Monday she backed down after the head of the nominally civilian government Thein Sein held firm over the oath, explaining it was the "desire of the people" to see her party in office after breakthrough April 1 by-elections.
As she left parliament, she was asked as to whether the ceremony had been an emotional occasion, Suu Kyi replied: "No, it was just interesting."
She was then whisked away by car to Naypyidaw airport to return to Yangon.
The international community greeted her election as a step towards democracy and had urged Suu Kyi, who drew huge crowds on the campaign trail, to take her seat amid fears her refusal could stall the transition from military rule.
UN chief Ban Ki-moon on Tuesday welcomed her climbdown over the oath, expressing hope of further cooperation between the NLD and Thein Sein's government.
In comments later echoed by the US State Department, Ban said his meetings in Myanmar this week with Thein Sein and the NLD leader had left him "convinced that they will continue to make progress."
Members of the NLD -- the main opposition force after securing 43 of the 44 seats it contested in April 1 by-elections -- flanked her during the short ceremony in Naypyidaw.
The party, which boycotted a controversial 2010 election, agreed to rejoin the political mainstream last year after a series of reforms by the government.
But it is still a minority influence in parliament with one quarter of the seats in both chambers reserved for unelected military officials.
Renaud Egreteau, a Myanmar expert from the University of Hong Kong, said Suu Kyi's retreat over the oath showed that compromise was now among her "political tools".
"Aung San Suu Kyi and the League (NLD) should not push themselves into paradoxes by agreeing to participate in the army's constitutional game while refusing the rules," he added.
Appearing alongside Ban after their near hour-long talks at her lakeside villa in Yangon on Tuesday, Suu Kyi said she was willing to compromise for the sake of reform.
"We have always believed in flexibility, in the political process... that is the only way in which we can achieve our goal without violence," she said.
The democracy icon, who was released from house arrest in 2010, has shown increased confidence in Thein Sein's government in recent weeks, calling for the suspension of EU sanctions and planning her first international trip in 24 years. (AFP)
