CPI-M workers had gathered in front of the Alipore Central jail when Seth, known in party circles as the Haldia strongman, was released 122 days after he was arrested.
A division bench of the Calcutta High Court, comprising Justices Ashim Kumar Roy and Tafiq Uddin, had granted bail to Seth on a personal bond of Rs 60,000.
Police said that as per the court order, Seth would have to report to Bhowanipore police station and would not be able to enter East Midnapore district, under which Haldia and Nandigram fall, till further orders.
Seth was also asked by the court to appear before the investigating officer twice a week.
Speaking to the media, Seth said he was happy to be freed, though on bail, but was saddened to know that many of his party colleagues were still in jail.
"I hope that they will also be released soon," he said. The CPI(M) leader said, "My release is victory of the people."
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Seth was arrested on March 17 from a Mumbai guest-house by the West Bengal CID along with two others - former CPI(M) MLA Ashok Guria and CPI(M) district committee member Amiya Sahu.
The CID came into the picture when the high court directed it to investigate the case of six missing Trinamool workers following habeas corpus petitions filed by their family members after the Mamata Banerjee government came to power in West Bengal.
The trio is accused of abduction and murder in connection with the attack on a peace rally by Bhumi Uchhed Pratirodh Committee on November 10, 2007 during the infamous 'recapture' of Nandigram.