His Cabinet was also sworn in the same day.
Amid cheers and the crowd shouting 'Inquilab Zindabad', Kejriwal took oath.
Delhi Lieutenant Governor Najeeb Jung administered the oath of office and secrecy to Kejriwal.
Earlier in the day, Kejriwal and other AAP leaders took a metro from Barakhambha Road Metro Station to Ramlila Maidan.
He garlanded at the metro station and given a hero's welcome.
Meanwhile, Gandhian social activist Anna Hazare has written to Kejriwal to congratulate him and convey his apology for not being able to be present at his swearing-in ceremony.
Former IPS officer and social activist Kiran Bedi tweeted: "May God protect Arvind, his team and Aam Admi who has driven the change in value systems in politics. Good for the entire country!"
While at 45 Kejriwal became the youngest chief minister of Delhi, his other ministers' list included the names of Manish Sisodia, Somnath Bharti, Satyendra Kumar Jain, Rakhi Birla, Saurabh Bhardwaj and Girish Soni.
Fifteen days after the Delhi assembly election results were declared, the AAP on Dec 23 said it will form the government with the support of the Congress party in the national capital.
The just-over-a-year-old party led by Kejriwal emerged as the second biggest outfit with 28 seats, falling only a few seats short of the right wing BJP and allies who managed 32 seats.
The BJP is four short of a majority in the 70-member Delhi assembly. Congress managed only 8 seats.
--IBNS (Posted on 28-12-2013)