Hariri was born on 1 November 1944 to a modest Sunni Muslim family in the Lebanese port city of Sidon. He had two siblings (brother Shafic and sister Bahia) He attended elementary and secondary school in Sidon, and graduated in Business administration from Beirut Arab University.

Hariri married twice. He had seven children. In 1965, he married an Iraqi woman, Nidal Bustani, who is the mother of his three sons; Bahaa (born 1967), who is a businessman, Saad, who succeeded his father as leader of the Future movement, and Houssam—who died in a traffic accident in the US in the late 1980s. They divorced. He married his second spouse, Nazik Audi, in 1976 and she is the mother of four of Hariri's children, including Ayman Hariri, Fahd Hariri and Hind Hariri.

In 1969, Hariri established Ciconest, a small subcontracting firm, which soon went out of Business. He then went in Business with the French construction firm Oger for the construction of a hotel in Ta’if, Saudi Arabia, the timely construction of which earned praise from King Khaled. Hariri took over Oger, forming Saudi Oger, which became the main construction firm used by the Saudi Royal family for all their important developments. As a result, a few years after his first contract with King Khaled, Hariri had become a multi-billionaire.

Having accumulated his wealth, Hariri started a number of philanthropic projects, including the building of educational facilities in Lebanon. His first initiative in Lebanon was the Islamic Association for Culture and Education, which he founded in 1979. The association was later renamed the Hariri Foundation. Hariri became progressively more embroiled in politics. His appeals to the United Nations and services as an emissary to the Saudi Royal family won him international recognition on the political stage for his humanitarian efforts.

Hariri returned to Lebanon in the early 1980s as a wealthy man and began to build a name for himself by making large donations and contributions to various groups in Lebanon. However, he continued to serve as a political advisor to Prince Bandar bin Sultan in 1983. He was implanted as the Saudis' strong man following the collapse of the PLO and the paucity of any viable Sunni leadership in the country as well as a response to the rising power of the Shiite militia Amal. As a former Saudi diplomatic representative, he played a significant role in constructing the 1990 Taif Agreement that ended Lebanon's sixteen-year civil war. In 1992, Hariri became the first post-civil war prime minister of Lebanon under President Elias Hrawi. Hariri put the country back on the financial map through the issuing of Eurobonds and won plaudits from the World Bank for his plan to borrow reconstruction money as the country's debt grew to become the largest per capita in the world. His first premiership lasted until 1998, and Hariri was replaced by Salim Hoss as prime minister. In fact, as a result of the power struggle between Hariri and newly elected President Émile Lahoud, he left office.

From 1982 until his death Hariri owned 2–8a Rutland Gate a large house in London's Knightsbridge district. The house was gifted to the Crown Prince of Saudi Arabia, Sultan bin Abdulaziz, after Hariri's assassination.

Hariri was considered as the principal actor in the widespread corruption that plagued Lebanon during the Syrian occupation. His wealth grew from less than $1 billion when he was appointed prime minister in 1992, to over $16 billion when he died. The Company for the Development and Reconstruction of Beirut's Central District, known as Solidere, in which Hariri is the primary shareholder, expropriated most property in the central Business district of Beirut, compensating each owner with shares in the company, were worth as little as 15% of the property's value. That Hariri and his Business associates profited immensely from this project was an open secret.

As result of the growing criticism and popular discontent with Hariri's policies, the government banned public demonstrations in 1994 and relied upon the Army to enforce the decree. In return for a relatively free hand in economic matters, Hariri cooperated with Syria's drive to consolidate its control over Lebanon. Under the guise of "regulating" the audiovisual media, the government placed control of all major television and radio stations in the hands of pro-Syrian elites. Supporters of Michel Aoun were also perpetually harassed and detained.

The last and perhaps most significant aspect of "Horizon 2000" was economic stimulus via foreign direct investment. Specifically, Hariri supported foreign firms and individuals taking an interest in Lebanon's developmental potential. Hariri simplified tax codes and provided tax breaks to foreign Investors. Due to his previous successes in the private sector and the numerous resulting international connections, Hariri was able to garner a significant amount of low-interest loans from foreign Investors. Hariri also pursued aggressive macroeconomic policy such as maintaining strict regulations on bank reserves and inter-bank interest rates to curb inflation and raise the value of the Lebanese pound relative to the dollar.

During a BBC interview in 2001, Harīrī was asked by Tim Sebastian why he refused to hand over members of Hezbollah that were accused by America of being terrorists. He responded that Hezbollah were the ones protecting Lebanon against the Israeli occupation and called for implementation of passed United Nations resolutions against Israel. He was further accused of making the American coalition in the war on terrorism worthless and asked if he was ready for the consequences of his refusal, reminding him that George W. Bush had said: "Either you are with us, or you are with the terrorists." He replied that he had hoped there would be no consequences, but would deal with them if they arrive. Hariri further said that he opposed the killing of all humans – Israeli, Palestinian, Syrian or Lebanese – and believed in dialogue as a solution. He further went on to say that Syria would have to stay in Lebanon for protection of Lebanon until they are no longer needed and Lebanon asks them to leave.

Lebanese Druze leader Walid Jumblatt, a recent recruit of the anti-Syrian opposition, emboldened by popular anger and civic action now being called Lebanon's Cedar Revolution, alleged in the wake of the assassination that on 26 August 2004 Syrian President Bashar al-Assad threatened Hariri, saying "[President of Lebanon] Lahoud is me. ... If you and Chirac want me out of Lebanon, I will break Lebanon." He was quoted as saying "When I heard him telling us those words, I knew that it was his condemnation of death." This meeting between Hariri and Assad, which had been on 26 August 2004, lasted for just fifteen minutes.

Major General Jamil Al Sayyed, then head of Lebanese General Security, Brigadier General Mustafa Hamdan, Major General Ali Hajj and Brigadier General Raymond Azar were all arrested in August 2005 at the request of German prosecutor Detlev Mehlis, who was carrying out the UN investigation about the assassination. Sayyed was one of the persons who decided to assassinate Rafik Hariri according to a leaked draft version of the Mehlis report along with other Syrian high-rank intelligence and security officers and officials, namely Assef Shawkat, Maher Assad, Hassan Khalil and Bahjat Suleyman. However, later reports about the assassination did not repeat the allegations against Jamil Al Sayyed and other three Lebanese generals. Four Lebanese generals were held in Roumieh prison, northeast of Beirut from 2005 to 2009. They were released from the prison due to lack of evidence in 2009.

A 2006 report by Serge Brammertz indicated that DNA evidence collected from the crime scene suggests that the assassination might be the act of a young male suicide bomber.

Hezbollah accused Israel of the assassination of Hariri. According to Hezbollah officials, the assassination of Hariri was planned by the Mossad as a means of expelling the Syrian army from Lebanon. In August 2010, Hezbollah leader Hassan Nasrallah presented evidence, consisting of intercepted Israeli spy-drone video footage, which he said implicated Israel in the assassination of Hariri. After an altercation between male Tribunal staff and women at a gynecology clinic in October 2010, Hezbollah demanded that the Lebanese government stop all cooperation with the Special Tribunal, claiming the tribunal to be an infringement on Lebanese sovereignty by western governments. On 1 November 2010, a report was leaked by Al Akhbar, a local secular, leftist newspaper, stating that Hezbollah drafted plans for a quick takeover of the country in the case an indictment against its members is issued by the UN Special Tribunal. The report states that Hezbollah conducted a simulation of the plan on 28 October, immediately following a speech by its secretary general.

An indictment against alleged Hezbollah members Salim Jamil Ayyash, Mustafa Amine Badreddine, Hussein Hassan Oneissi, and Assad Hassan Sabra was issued and confirmed by the Pre-Trial Judge of the United Nations special tribunal (see Special Tribunal for Lebanon) in 2011. In February 2014, the case against Hassan Habib Merhi was joined with the Ayyash et al. case. Proceedings against the accused Mustafa Badreddine were terminated in July 2016 following credible reports of his death. Salim Jamil Ayyash, Hassan Habib Merhi, Hussein Hassan Oneissi, and Assad Hassan Sabra currently remain on trial in absentia.

In its first two reports in 2014, the United Nations International Independent Investigation Commission indicated that the Syrian government may be linked to the assassination. Lawyers tasked with prosecuting those responsible for the 2005 bombing said they had received evidence linking Bashar Assad's phone to the case. In its tenth report, the UNIIIC concluded “that a network of individuals acted in concert to carry out the assassination of Rafiq Hariri.”