The Rajouri Garden assembly by-election comes just weeks before the much-talked about Delhi civic polls which is crucial for the Aam Aadmi Party. The BJP is currently in charge of the civic bodies in Delhi.
Voting started at 8 AM and ends at 6 PM at 166 polling stations according to the directive of the Election Commission.
The seat fell vacant early this year after the AAP's Jarnail Singh quit as legislator to contest the Punjab Assembly poll against Shiromani Akali Dal (SAD) patriarch Parkash Singh Badal.
Since 1993, Rajouri Garden has been a Congress bastion with the exception of the last two elections when it voted the BJP-Akali Dal combine candidate in 2013, and in 2015, when the AAP won the seat.
This time, the AAP is fielding Harjeet Singh, a new face, while the Congress has fielding Meenakshi Chandela, who belongs to a politically influential family of the area.
Veteran Manjinder Singh is representing the BJP-SAD combine.
Along with Electronic Voting Machines, the reliability of which has been questioned by the AAP, voter-verifiable paper audit trail (VVPATs) are being used at all polling stations of the constituency.
The by-poll results will be declared on April 13.
(With inputs from PTI)