Nagaland Chief Minister Neiphiu Rio resigned on Saturday, ahead of the oath-taking on March 7.
Rio, a four-time chief minister, submitted his resignation to Governor La Ganesan at the Raj Bhavan.
"As my tenure has come to an end, I submitted a letter of resignation as Chief Minister of Nagaland to the Hon’ble Governor, Shri @LaGanesan," he tweeted.
Rio's NDPP won 25 seats in the 60-member assembly, while its partner BJP won 12 seats.
He is likely to stake to form the new government on Monday, ahead of Tuesday's swearing-in ceremony, which will be attended by Prime Minister Narendra Modi.