Former Assam MP Sushmita Dev, shortly after quitting the Congress, joined the TMC in Kolkata on Monday, in the presence of the party's national general secretary, Abhishek Banerjee.
Dev had been serving as the national spokesperson of the Congress and its women's wing chief.
Taking to Twitter, the TMC welcomed the former parliamentarian to its camp.
"We warmly welcome the former President of All India Mahila Congress @sushmitadevinc to our Trinamool family! Inspired by @MamataOfficial, she joins us today in the presence of our National General Secretary @abhishekaitc & Parliamentary Party Leader, Rajya Sabha, @derekobrienmp," the TMC wrote on its official Twitter handle.
Dev, who sent her resignation letter to Congress chief Sonia Gandhi on Sunday, has offered no reason for quitting the grand old party.
In her letter to Gandhi, Dev said she was beginning a "new chapter in my life of public service".
She visited TMC MP Abhishek Banerjee's office at Camac Street in Kolkata earlier in the day.
Sources in the TMC said Dev is likely to meet TMC supremo and West Bengal Chief Minister Mamata Banerjee at Nabanna later in the afternoon.