Here are 10 points to know about the rally:
This will be the first time Chief Minister Nitish Kumar shares a stage with the Prime Minister since May 2009, and the first joint rally by the NDA in Bihar since November 2005.
The Sankalp rally will also be PM Modi's maiden one at Gandhi Maidan since he became the Prime Minister. His last event here was in October 2013, in the run-up to the previous Lok Sabha poll. A series of blasts had occurred at the event, killing six and injuring 85 others.
As Mr Kumar was a staunch critic of the Prime Minister until two years ago, political analysts are waiting to hear what he will say in his support at the rally. They also want to know if PM Modi will succeed in pulling crowds comparable to what Rashtriya Janata Dal chief Lalu Yadav used to in the 1990s.
The district administration has made elaborate security arrangements to prevent untoward incidents at the rally. As many as 4,000 police personnel will be present at the venue today, and 60 door-frame metal detectors have already been installed.
The organisers are sparing no effort to ensure the rally's success. As many as 30 trains and 6,000 buses have been booked to bring people to the event. Mr Kumar has also helped publicise the event among his supporters.
After the rally, the ruling parties in Bihar are likely to finalise the seats for the Lok Sabha elections. Although they have decided on a 17:17:6 formula between the three allies, the allotment of specific seats to parties is yet to be done.
Opposition leader Tejashwi Yadav had earlier demanded that the rally be called off because the bodies of CRPF soldiers killed in Kashmir's Pulwama on February 14 were still coming in. As the event drew closer, he released past videos of PM Modi and Mr Kumar taking potshots at each other.
The seat-sharing arrangement Bihar's grand alliance - comprising the Congress, RJD, Rashtriya Lok Samta Party, Hindustani Awam Morcha and Vikassheel Insaan Party - will also be finalised after the event.
The days preceding the Sankalp Rally saw the ruling leaders go on a foundation-laying spree. However, two promises made by the Prime Minister - providing special status to Bihar and establishment of a second AIIMS institute - continue to hang in balance.
Congress president Rahul Gandhi had addressed his party's Jan Akanksha (people's expectations) Rally at the same venue on February 3. Many leaders of the Grand Alliance had participated in the event.
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