He will replace former Congressman and Leader of Opposition Radhakrishna Vikhe-Patil, who switched over to the ruling Bharatiya Janata Party and was inducted into the Devendra Fadnavis ministry this morning.
"All Opposition parties have on Sunday submitted a formal letter to Assembly Speaker Haribhau Bagade, proposing Wadettiwar as the new Leader of Opposition," Congress Deputy Party Leader Naseem Khan told .
After a meeting at the home of Leader of Opposition in Council, Dhananjay Munde of the Nationalist Congress Party, a delegation of opposition leaders including Congress Legislature Party leader Balasaheb Thorat, and from the NCP, PWP and other opposition parties, met Bagade to deliver the letter, he added.
The Congress had named Wadettiwar as Leader of Opposition two days back, and now he will be formally named to the key post.
A legislator from Brahmapuri, he has been rewarded with the coveted post - which enjoys a Cabinet Minister status - for saving the Congress from a total wipe-out in the state in the recent Lok Sabha elections.
Appointed in-charge of Chandrapur and Gadchiroli districts, he managed to rope in Shiv Sena's Warora legislator, Suresh Dhanorkar to the Congress fold, barely weeks before the elections.
Dhanorkar was given the Congress ticket for Chandrapur and emerged a giant-killer - defeating Bharatiya Janata Party's strongman and Union Minister Hansraj Ahir to help the party secure one Lok Sabha seat from the state.
Wadettiwar, 57, will be third Leader of Opposition in the Maharashtra Assembly since 2014.
The post was first held by Shiv Sena's Eknath Shinde briefly before the party joined the government in late 2014.
Later, the post went to Congress' Vikhe-Patil, till he left the party and now joined the government on Sunday.
The final session of Maharashtra Legislature begins here on Monday, before the state goes to elections within next four months.
The combined Opposition boycotted the customary assembly session-eve meeting hosted by Fadnavis, making it the third consecutive time in the past one year.
( With inputs from IANS )