Ms Singh will contest against Rashtriya Lok Dal's Begum Tabassum Hasan, who is being backed by Akhilesh Yadav's Samajwadi Party, the Congress and Nishad Party. While Mayawati's Bahujan Samaj Party or BSP is supporting the RLD candidate, the party has not made it official.
Tabassum Hasan joined politics after the death of her husband in a road accident in 2008. In 2009, she was elected to parliament as a BSP lawmaker. She later joined the Samajwadi Party and eventually, the RLD.
Poll results will be declared three days later, and the opposition hopes to replicate the success of Gorakhpur and Phulpur - where the Samajwadi Party joined hands with its rival Bahujan Samaj Party to defeat the ruling BJP, clinching the former seat of UP Chief Minister Yogi Adityanath.
Last week, the opposition received a big boost when Tabassum Hasan's brother-in-law, Kanwar Hasan -- contesting as an independent candidate -- dropped out, eliminating the risk of dividing the Muslim votes. Muslims, Jats and Dalit form a significant part of the electorate in a constituency with nearly 17 lakh voters.
Jats are the core supporters of the Rashtriya Janata Dal. By fielding a Muslim candidate, the party as well as the opposition hopes to unite its Jat base, which shifted loyalties to the BJP after Muzaffarnagar riots in 2013, with Muslim voters.
Hoping to retain the seat, the BJP has led a fierce campaign in Kairana, with both Chief Minister Yogi Adityanath and his deputy addressing rallies in Saharanpur and Shamli. Several ministers in Yogi Adityanath's cabinet were also asked to campaign for the party in the run-up to the by-polls.
The reported exodus of Hindus from Kairana in 2016 has also emerged as a contentious issue, with the RLD leader rejecting claims of exodus, dismissing it as propaganda. BJP's Mriganka Singh has said that though hundreds of Hindus fled from the Kairana before the 2017 assembly election in UP, it has stopped now.
Four Lok Sabha by-elections and ten assembly by-elections will be held in ten states tomorrow. Apart from Kairana, assembly by-polls will also be held in Noorpur constituency of Uttar Pradesh.
Election Results for Lok Sabha Election 2019 will be out on May 23. Get the latest election news and live updates on ndtv.com/elections. Catch all the action on NDTV Live. Like us on Facebook or follow us on Twitter and Instagram for news updates from each of the 543 parliamentary seats for the election 2019