The volunteer, identified as Ashok Mann, was accompanying Mehrauli MLA Naresh Yadav in his convoy when shots were fired. A second volunteer Harinder was also injured and the MLA escaped unhurt.
Yadav called the incident "unfortunate" and demanded a thorough investigation.
Winning MLA visited temple; bullets were fired on way back
In an open jeep, Yadav was returning from a temple in Kishangarh village when an unidentified man approached the convoy.
According to the politician, at least four rounds were fired. Mann was rushed to Fortis Hospital where he died. Hospital authorities confirmed that two men were brought in, but didn't divulge details about Harinder.
Reportedly, six-seven bullet shells were recovered from the crime scene.
Yadav doesn't know why his convoy was attacked
"I do not know the reason behind the attack but it happened all of a sudden. Around 4 rounds were fired. The vehicle I was in was attacked. I am sure if police inquires properly, they will be able to identify the assailant," Yadav said.
I could have been killed: Yadav
Yadav, who defeated BJP's Kusum Khatri by a margin of 18,161 votes, said he could have been killed in the attack.
"Two people were shot in which Ashok Ji has died and Harinder Ji was injured. I do not know whether they attacked me in particular but they certainly targeted our convoy. Anybody could have been shot in this attack including me," he said.
Sanjay Singh shed light on poor law and order situation
AAP leader Sanjay Singh condemned the attack by tweeting in Hindi, "The brazen murder of Ashok Mann after an attack on Mehrauli MLA Naresh Yadav- this is the rule of law in Delhi, Naresh Yadav was returning from a temple."
The Delhi Police comes under Home Ministry and has been a bone of contention between the state government and the Centre.
Meanwhile, police said Yadav wasn't the target
On the attack, police said Yadav was not the target of the assailant.
"The investigation so far reveals that there was one assailant. Naresh Yadav wasn't the target. The assailant had specifically come to target the man who was shot dead (AAP volunteer)," said Southwest Additional DCP Ingit Pratap Singh.
The FIR in this incident was registered at Kishangarh police station.