But his father's killing in a February bomb blast propelled the 35-year-old tycoon to political centre stage, with his list set to sweep the first round of Lebanon's elections after many rivals stood aside, even before voting began on Sunday.
"I don't kid myself," he told CNN on election day. "I know that people are sympathising with us. People are going to the voting booths for my father. I think I am merely am a symbol for now. I need to work hard the coming four years to ... fill a little bit my father's shoes."
Indeed, the lists headed by Saad, who took over his father's Future party, are even called the "Martyred Prime Minister Rafik al-Hariri" lists.
Saad (C) was chosen over his
elder brother Bahaa
Supporters of Saad, Rafik al-Hariri's second son by his first Iraqi wife, are expected to scoop all 19 seats in Beirut in the first round of the four-stage elections.
Already a success of his own in the business world, Saad was chosen to continue the "national and political mission" of his billionaire father, who was credited with rebuilding Lebanon after the devastating 1975-1990 civil war.
Sources close to the al-Hariri family say they tapped Saad because he has more charisma and is better at interacting with people than his eldest brother Bahaa.
Saad is a business graduate of Georgetown University in Washington and heads his father's Saudi-based construction firm, Saudi Oger, one of the largest companies in the Middle East which has a turnover of more than $2 billion and employs about 35,000 people.
Al-Hariri empire, which has been managed by Saad since 1996, also spans banking, real estate and media through companies such as Saudi Investment Bank, Saudi Research and Marketing Group, and Future Television.
"Because of his lack of exposure to the corrupt reality of the Lebanese state, he has the means to resist negative aspects of governance that are so prevalent here"
Daily Star newspaper,
He also has his own real estate firm worth an estimated $145 million.
Saad was born in April 1970, and is married with two young children. His wife, Lara Bashir Al-Adem, hails from a prestigious Syrian family.
Though he lacks political experience, the typically soft-spoken Saad has taken his father's reigns with ease.
The Daily Star labelled him an "unlikely" candidate whose "inexperience in walking the crooked paths of the Lebanese political environment is not a detriment but rather an asset".
"Because of his lack of exposure to the corrupt reality of the Lebanese state, he has the means to resist negative aspects of governance that are so prevalent here," the newspaper said.