Chirac, a colossal figure in France's politics for three decades, died at the age of 86, on Thursday.
His time as head of state from 1995-2007 saw France play a leading role in Lebanon, most notably in 2005, when he helped lead international efforts to push Syrian troops out of the country.
"Today, the world lost one of France's greatest men," Saad Hariri said in a statement released by his office.
"He held Lebanon's hand during its toughest times and was always at the forefront when it came to defending the country's freedom, sovereignty and independence," he added.
The prime minister said that Chirac's death also marked a great loss to his family.
The Hariri family has long-standing ties to the former French president, going back to the early 1980s when Chirac, then the mayor of Paris, became close to Saad Hariri's father Rafiq.
Chirac's death marks a "special loss of a dear friend, who was the spiritual twin" of Rafiq Hariri "and a big brother to my family," the Lebanese prime minister said.
The elder Hariri, a wealthy real estate developer who made his fortune in Saudi Arabia, made numerous investments in France and headquartered his construction group Oger International in a Parisian suburb.
Rafiq Hariri's friendship with Chirac turned overtly political after 1992 when he became prime minister of Lebanon. Chirac was elected president three years later.
He was the only Western head of state to attend Hariri's funeral in Beirut in 2005 after he was killed in a bombing.
Chirac lived in a luxurious Paris apartment owned by the Hariri family for around eight years after he left office and retired in 2007.
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