A visibly moved Michel Thierry Atangana, 49, stepped off the plane and met his family, including his two sons aged 19 and 23, and said he was "extremely worn out."
His detention had drawn appeals from French President Francois Hollande who termed it "unacceptable" and the UN rights agency which denounced the "inhuman conditions" under which he was being held.
"The ordeal was one that you cannot imagine," said Atangana, who was born in Cameroon and acquired French nationality after marriage.
"I need time for introspection before I can express myself as a free man," he said.
"He was held in isolation in a cell that was too small for him. He couldn't even stand up straight," his lawyer Eric Dupond-Moretti told reporters.
"I am virtually seeing him for the first time in my life today," said Eric, Atangana's 23-year-old son.
"We will take time to know each other and to rebuild our relationship," he said.
Eric Atangana was only six when his father was imprisoned.
Atangana was released after Cameroon's long-serving President Paul Biya, who critics accuse of being authoritarian, signed a decree on February 18 pardoning prisoners sentenced for more than ten years on charges of embezzling public funds.
Atangana, who was sent to Cameroon by his employers in connection with a highway development project in 1994, was arrested in 1997 -- a little after the detention of a Biya loyalist-turned-foe Titus Edzoa.
Before their imprisonment, Edzoa resigned from cabinet and announced he would challenge Biya in the 1997 election. Atangana was his campaign manager.
Edzoa was released on Monday along with Atangana.
Atangana was sentenced to 15 years in prison in 1997 and then sentenced again in 2012 to 20 years, despite a huge outcry from rights groups.
He has consistently denied stealing public funds.