Hagai Amir, who helped his brother Yigal Amir plot the assassination of Yitzhak Rabin, was released from prison.
Authorities at the Ayalon prison in Ramle, in central Israel, released Amir, 43, on Friday morning.
He had been in prison 16 years and has never expressed remorse for his role in the Nov. 4 1995 murder of the Israeli prime minister by his brother, a right-wing extremist.
Protesters gathered outside the prison. He greeted them with a "v" sign.
Amir planned to spend his first Sabbath after his jail sentence with a friend at the Shave Shomron settlement, although media quoted its residents as saying he would not be welcome.
Yigal Amir is serving a life sentence at Eshel prison in Beersheba. Another coconspirator, Dror Adani, completed his sentence in 2002.