The man identified as Lali, who is an autorickshaw driver, first garlanded Arvind Kejriwal and then slapped him following which the attacker was thrashed by AAP supporters.
AAP leader Manish Sisodia tweeted that Kejriwal was injured in his eye. Kejriwal's spectacles fell on the ground following the attack.
The 38-year-old attacker, a resident of Aman Vihar in Outer Delhi, has accused Arvind Kejriwal of not fulfilling promises made to the auto-drivers. He was later detained by the police.
"I do not understand why do some people resort to violence for becoming the Prime Minister. If you think by attacking us, we will keep quite then you are wrong. We will fight this battle till the last breath," Kejriwal said.
Later in a tweet, Arvind Kejriwal said, "I am just thinking - why am i being repeatedly attacked Who r (are) the masterminds What do they want What do they achieve"
The AAP leader headed for Rajghat after the attack which has been condemned by both BJP and Congress.
"No one should slap anyone. This is against democracy. We do not support it," Congress leader Kapil Sibal said.
BJP Vijay Goel also criticised the attack on the AAP leader. "We do not approve such things. But there is one thing that there has been more opposition to AAP because they say something and do something else."
AAP's Sisodia said people affected by AAP movement were trying to derail it.
"The people who indulge in politics of caste and religion, those who are involved in corruption are afraid of AAP. The politics in the country is changing and that is why they are resorting to such acts," he said.
This was second such attack on Arvind Kejriwal in the last four days. He was attacked by a 19-year-old youth during his campaigning in Dakshinpuri area of South Delhi on Friday.
The former Chief Minister has been attacked a number of times in the past.
On March 28, he was attacked by a man, who claimed to be a supporter of Anna Hazare, during his election rally in Haryana.
In Varanasi last month, protesters threw ink on Arvind Kejriwal and a number of other party leaders.