The Supreme Court had granted him bail.
Speaking to mediapersons outside the jail premises, Perarivalan and his mother Arputham Ammal thanked everyone "who stood with them in their fight for justice".
Arputham Ammal said, "This is an important phase in the 31 years of fight for justice. This bail is an interim relief and my fight will continue with your support until my son and all other prisoners - in this case - are released from jail."
She also thanked the Tamil Nadu Chief Minister, M.K. Stalin, Opposition leader and former Chief Minister, Edappady K. Palaniswami, and other "who stood by her".
Perarivalan's mother said, "I would like to recall the name of Sengodi (who had immolated herself against the capital punishment awarded to Rajiv Gandhi assassination convicts including Perarivalan), who gave her life for the cause and I do thank the media, lawyers, and human rights activists at this moment."
She said that she and Perarivalan will "meet everyone who stood by them".
Perarivalan was arrested in June 1991 and served 31 years of prison term.
Justices Nageswar Rao and B.R. Gavai of the Supreme Court had granted him bail taking note of the petition by Perarivalan's lawyers that he had served more than 30 years in prison.