Vacated with the appointment of former Assam Chief Minister Sarbananda Sonowal as Union Minister last year, the Majuli constituency will hold a by-election on March 7.
Mr Sonowal, 59, had resigned from the assembly seat after being elected to the Rajya Sabha last year.
The formal notification for the by-poll will be issued on Thursday, according to the schedule announced by the Election Commission.
The counting of votes will take place on March 10 along with Uttar Pradesh, Uttarakhand, Goa, Punjab and Manipur assembly elections.
The five states will in phases vote from February 10 to March 7.
The seventh and last phase of assembly elections in UP will be held on March 7.
Majuli is the world's largest river island and it got the status of a district when Mr Sonowal was the Assam Chief Minister.
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