Markio Tado represented Tali constituency in Kra Daadi district of the BJP-ruled state.
"The Congress has no vision for the future of the state. So I joined the BJP in the larger interest of the state and the people of my constituency," he told a press conference.
The state has witnessed rapid development under the Pema Khandu government, he claimed.
Tado had won from Tali as a Peoples' Party of Arunachal candidate in the 2009 Assembly elections and as a Congress nominee in the 2014 polls.
The MLA asserted that he would not contest the election this time and extend his unconditional support to an aspiring BJP candidate.
With Tado resigning, the Congress in the state has left with four legislators in the house of 60.
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