Two of his associates were also critically injured in the incident which took place at around 8:10 pm when Singh was attending a religious programme at Abhinandan Vatika in Najafgarh.
38-year-old Singh was attacked by over six armed men who had reached the spot in a SUV. At least 15-20 rounds of bullets were fired.
Singh was the younger brother of local strongman Kishen Pehalwan, who has more than two dozen criminal cases registered against him, police said.
Officials said that prima facie it seems to be a case of gang war and needle of suspicion is towards the gang of local criminal Udayveer alias Kaale, who was recently released from jail.
A senior police officer said that all the three injured were rushed to Medanta hospital in Gurgaon, where Singh succumbed to his injuries while condition of the other two-- Singh's personal security officers (PSO)-- is critical.
Eyewitnesses claimed that Singh was shot in the head from very close range.
"He has been declared dead by doctors," Joint Commissioner of Police (southwestern range) Tajendra Luthra told PTI.
Crime and FSL teams picked up circumstantial evidence from the spot and several teams including those from the Special Cell and Crime Branch have been deployed to crack the case.
A similar attack had taken place on Singh in June 2012. He was shot at by assailants outside his office in a south west Delhi locality.
One of his relatives had also received bullet injury at that time. Singh had survived two bullet injuries one in his left shoulder and another in his abdomen.
In that police had arrested four persons, who are facing trial in the case.
(With inputs from agencies)