The swearing-in ceremony in the capital Naypyitaw marks the first time the 66-year-old opposition leader has held public office since launching her struggle against authoritarian rule nearly a quarter century ago.
Ms Suu Kyi's entry into the legislature heralds a historic new political era for the Southeast Asian nation, cementing a risky detente between her party and the reformist government of President Thein Sein.
However her National League for Democracy party will occupy too few seats to have any real power in the ruling-party dominated assembly.
There are fears the presence of the opposition politicians could simply legitimise the regime without any change.