A ticket was bought with money received from a friend and the French Embassy in Kathmandu prepared the necessary travel documents allowing him to board the flight on Friday evening, lawyer Gopal Siwakoti Chitan said.
Sobhraj was driven from Kathmandu Central Jail in a heavily guarded police convoy earlier on Friday to the Immigration Ministry.
The Supreme Court had ordered that Sobhraj, who was sentenced to life in prison, be released due to poor health, good behavior and having served more than 75% of his sentence, which makes him eligible for release. He said Sobhraj had heart disease.
Life sentences in Nepal are 20 years.
The order also stipulated that he must leave the country within 15 days.
Sobhraj has in the past admitted to killing several Western tourists. He is believed to have killed at least 20 people in Afghanistan, India, Thailand, Turkey, Nepal, Iran and Hong Kong in the 1970s. His 2004 conviction in Nepal was the first time he was found guilty before a tribunal.
Sobhraj had previously been held for two decades in the maximum security Tihar prison in New Delhi on suspicion of theft, but was deported without charge to France in 1997. He resurfaced in September 2003 in Kathmandu.
His nickname, The Serpent, stems from his reputation as an artist of disguise and escape.
French officials have not publicly commented on his expected return.