The launch at Delhi's Constitution Club was attended by TMC's Dinesh Trivedi, Congress' Renuka Chowdhary, NCP's Majeed Memon and Pavan Varma, RLD's Jayant Chaudhary and AAP's Ashutosh and Sanjay Singh were present . Former diplomat and analyst KC Singh played a key as an MC of this event.
The only significant omission was the Left Front, where the faultlines in CPM leadership recently showed over the battle between factions led by Sitaram Yechury and Prakash Karat over joining forces with the Congress to oust BJP in the national elections next year.
Yashwant Sinha, however, did not rule out the possibility of Left's eventual participation, saying it was an "evolving" forum.
Loose in its definition, the National Forum will look into everything from the agrarian crisis to diplomacy and internal security. It would also provide a platform for Mr Sinha, who has been highlighting the shortcomings of the government.
Its first big day will be February 1, when the government will present the Union budget in parliament.
The BJP has accused Mr Sinha of "spreading pessimism" out of "frustration" after he blamed the downturn in economy on demonetisation and what he called the faulty implementation of the flagship Goods and Services Tax. The other BJP leader in the forum, Shatrughan Sinha, is known for his frequent reproaches to the party and Prime Minister Narendra Modi - which the BJP has largely ignored.
Yashwant Sinha today took on the government on its foreign policy - seen as one of the biggest areas of its success.
"Foreign policy is apparently our biggest achievement. Whenever someone shows Indian passport, they are saluted! But look what happened with Doklam and China," Mr Sinha said. "Pakistan and even old allies like Russia becoming detached - foreign policy of government in tatters... There is fear in our party just not with me and Shatrughan. Speaking the truth is blasphemy."