The seat, which fell vacant following the demise of actor-turned-politician Vinod Khanna of the BJP in April, is expected to witness a three-horse race between the Congress, the BJP and the AAP.
While the Congress has fielded its Punjab unit chief Sunil Jakhar, the BJP has put up businessman Swaran Salaria.
The AAP has placed a bet on Major General (retd) Suresh Khajuria.
As many as 15.22 lakh voters are eligible to exercise their franchise in the by-election being fought by 11 candidates.
Of the total electorate of 15,22,922 in the constituency, 7,12,077 are women and 14 belong to a third gender, official said.
Around 30 companies of paramilitary forces and 7,000 Punjab police personnel have been deployed in the constituency.
The voting will start at 8 am and will go on till 5 pm.
A total of 1,781 polling stations have been set up at 1,257 locations, of which 457 have been declared vulnerable and 83 critical.
Voter-verified paper audit trail (VVPAT) will be used at all polling stations. Votes will be counted on October 15 and the result will be declared the same day, the official said.
The bypoll will gauge the popularity of the Amarinder Singh government which is battling allegations of reneging on its pre-assembly polls promise of farm debt waiver and free smartphones.
The Congress, which had bagged 77 seats in the 117-member Punjab Assembly in February, is keen to keep the winning momentum going.
The BJP has also tried pulling out all the stops to retain the seat, which Khanna had won four times.
A victory would give much-needed boost to the BJP, which had bagged just one segment of Sujanpur out of the four seats it had contested in the assembly polls.
The Gurdaspur Lok Sabha seat has nine assembly segments.
The BJP's win will also provide a breather to its ally Shiromani Akali Dal, which had been relegated to the third spot in the assembly polls.
The AAP, the main opposition party in Punjab with 20 seats in the House, is also looking to strengthen its presence in the state.
Meanwhile, the Election Commission today said it has allowed the use of alternative identity cards for the by-poll.
A spokesperson of the office of the chief electoral officer, Punjab, said those not having voter IDs can vote using documents such as Aadhaar card, passport, driving licence or service ID cards issued by the central and state governments or public sector undertakings.
The poll panel has also allowed bank or post office passbooks with photographs, PAN card, MGNREGA job card, health insurance smart card, pension documents and authenticated voter slips to be used as identity proof.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)