Nicolas Sarkozy will become the first French ex-president to go to jail, starting a five-year sentence for conspiring to fund his election campaign with money from late Libyan dictator Muammar Gaddafi.
Not since World War Two Nazi collaborationist leader Philippe Pétain was jailed for treason in 1945 has any French ex-leader gone behind bars.
Sarkozy, who served as president from 2007-2012, has appealed against his jail term at La Santé prison, where he will occupy a cell measuring about 9 sq m (95 sq ft) in the jail's isolation wing.
More than 100 people stood outside the jail after his son Louis called for supporters to gather in solidarity. Another son, Pierre, requested a message of love and support.
Sarkozy, 70, was due to arrive at 10:00 (08:00 GMT) at the infamous 19th-century prison in Montparnasse and has consistently denied any wrongdoing in connection with the alleged Libyan funding affair.
His conviction stems from a case alleging that his 2007 presidential campaign was funded by millions of euros in cash from Libya, though he was cleared of personally receiving the money.
Throughout his incarceration, Sarkozy has been placed in isolation for his safety, as other inmates are noted for serious offences. He has expressed his willingness to endure prison conditions, announcing he will be taking books with him, including a life of Jesus and The Count of Monte Cristo, which tells the tale of a man unjustly imprisoned.
In previous media interviews, Sarkozy affirmed, I'm not afraid of prison. I'll keep my head held high, including at the prison gates. He has been vocal about his innocence and continues to fight the charges against him.
In the unusual measure of official support, Justice Minister Gérald Darmanin stated he would visit Sarkozy in prison, acknowledging the man's distress during this challenging time.
