46-year-old Kejriwal was first to take oath followed by Deputy Chief Minister Manish Sisodia and other Ministers.
Pro-tem Speaker Fateh Singh administered the oath of office and secrecy to the MLAs.
AAP had won a whopping 67 seats in the Assembly polls while BJP got only 3 seats in the 70-member House.
The two-day session has been convened, basically, for oath-taking by the MLAs and election of the Speaker and Deputy Speaker.
It was not clear whether the AAP government will offer the post of the Leader of Opposition to BJP.