At the close of the deadline for withdrawal, all the three contestants - Singh, who is the first Congress candidate, Santius Kujur, the party's second candidate and AIUDF's Aminul Islam remained in the fray.
The nomination papers of the three contestants were found valid on the day of scrutiny on May 21 and no nomination was withdrawn today.
Polling would be held on May 30 from 9 am to 4 pm and votes would be counted the same day at 5 pm. The election process will be completed before June 3 as per the Election Commission's May 13 notification.
The prime minister's victory is certain as he is the only contestant for the first preference votes of 78 Congress MLAs in the 126-member Assembly, while Kujur and Islam are vying for the second seat.
Badruddin Ajmal, the chief of All India United Democratic Front (AIUDF), which is the second largest party in the Assembly with 18 seats, has said that as partners in the UPA coalition at the Centre the party respects the prime minister and wants him to win unopposed but at the same time it was keen to fight till the end for the second seat.
Singh's four sets of nomination papers which were endorsed by 40 MLAs were found in order. Singh had, however, filed a fresh affidavit two days before scrutiny correcting his age in his nomination papers as 80 years and not 82.
Kujur, who had contested the last assembly polls from Panery in Udalguri district, is an adivasi leader from the Christian community, while Islam is AIUDF's general secretary and an advocate in Gauhati High Court.