Hamad was born in Doha, Qatar, on 11 January 1959. He is the fifth son of Jassim bin Jabr al Thani. Through his Father, he is the grandson of Jabr bin Mohammed al Thani. Jabr was a younger brother of Jassim bin Mohammed al Thani, the founding Father of the modern Qatar .

In 1982, Hamad married Jawaher bint Fahad al Thani. He subsequently married Noor al Subaie, the daughter of the former minister of education, in 1996 as his second wife.

Of other humanitarian initiatives, he has facilitated the release of prisoners, including the five Lebanese prisoners in Eritrea. He supported the effort to release Mr. Nawaz Sharif, the former Prime Minister of Pakistan from jail, and was instrumental in freeing the Bulgarian Nurses in Libya from prison. He has opened Qatar to political refugees in the Muslim and Arab worlds. During the Bosnian conflict of the 1990s, he secured large quantities of food, Medicine and other items to the Bosnian population.

On 1 September 1992, Hamad was appointed as foreign minister of Qatar by the 8th Emir. He was retained in his post when the Emir's son, Hamad bin Khalifa al Thani came to power in a coup in 1995. Hamad played an important role in the overthrow of the 8th Emir. On 16 September 2003, Hamad was appointed first deputy prime minister while retaining his position of minister of foreign affairs. On 2 April 2007, he was appointed as prime minister, following the resignation of Abdullah bin Khalifa al Thani; Hamad also continued to serve as foreign minister. HBJ had vast foreign policy goals for Qatar during his tenure. Qatar was said to be "punching above its weight" under HBJ’s direction, but the foreign ministry was generally regarded as lacking the necessary infrastructure to live up to his aspirations.

Hamad facilitated the agreement that led to a unity constitution in Yemen in May 1990, ratified by the populace in May 1991. It affirmed Yemen's commitment to free elections, a multiparty political system, the right to own private property, equality under the law, and respect of basic human rights. Parliamentary elections were held on 27 April 1993.

In 1996, he worked to settle a brief war between Eritrea and Yemen over the Hanish Islands. As part of the agreement to cease hostilities the two nations agreed, through the negotiating effort of Hamad, to refer the issue to the Permanent Court of Arbitration at The Hague in 1998. Yemen was granted full ownership of the larger islands while Eritrea was awarded the peripheral islands to the southwest of the larger islands. Since then relations between the two governments have remained relatively normal.

Hamad was instrumental in creating the peace settlement between Sudan and Eritrea in 1998. The un-demarcated border with Sudan had posed a Problem for Eritrean external relations for most of the nation's existence. He negotiated a peace settlement between Sudan and Eritrea. After the agreement was signed, relations somewhat normalized.

Following courting by Michael Portillo, Qatar entered into an arms deal worth £500 million with BAE Systems. £7 million was transferred into two trusts in Jersey of which Hamad was named as a beneficiary. In an attempt to prevent money Laundering the funds were frozen from 16 July 2000 by the Jersey Financial Services Commission, who then began a court case and investigation. Hamad paid the Jersey authorities £6 million as a "voluntary reparation" as "the structures put in place by his advisers may have contributed to the cost and complexity of the inquiry." The case was then dropped by the Jersey authorities.

In 2009, he assisted in the settlement agreement between Sudan and Chad. The civil war in Chad began in December 2005. On February 8, 2006 the Tripoli Agreement was signed, which temporarily stopped the fighting. However, hostilities resumed after two months, leading to several new agreement attempts and a final settlement between the two parties in 2009.

In 2007, Hamad helped organize the Lebanese national dialogue and the peace agreement between various Lebanese political groups to end the worst internal fighting in Lebanon since the civil war of 1975–1990. In an attempt to resolve a broader political showdown that had paralyzed the country for 18 months, Hamad summoned the Lebanese government and Hezbollah-led opposition to Qatar for talks. He declared an agreement sponsored by the Arab League to deal with the Lebanese crisis. In the agreement the parties pledged, “to refrain from returning to the use of weapons or violence to realize political gains." The Lebanese government furthermore committed itself to introduce a new electoral law designed to provide better representation in the country's sectarian system of power sharing.

A May 2008 diplomatic cable sent by then U.S. chargé d'affaires in Doha, alluded to a dispute between HBJ and the Qatari intelligence officials over a Qatari senior bank official imprisoned for 6 months over his role in funding Khalid Sheikh Mohammed (KSM), the al-Qaeda mastermind of September 11. The senior bank official was Khalifa Muhammad Turki al-Subaiy who financed KSM while working at Qatar Central Bank.

HBJ is facing a lawsuit brought on by Fawaz Al-Attiya, former official spokesman for Qatar, who says that agents acting on behalf of HBJ imprisoned and tortured him in Doha for 15 months from 2009–2011. Al-Attiya says that he was kept in solitary confinement, only let out of handcuffs to be interrogated, subjected to sleep deprivation, and denied proper access to food, water, and sunlight. Al-Attiya also alleged that he was not adequately compensated for his Qatari land that was expropriated by the state. Documents submitted by Al-Attiya’s lawyers state that in 1997, HBJ offered to buy 20,000 square meters of land from Al-Attiya in west Doha. Al-Attiya says that he refused the offer because he felt that the land was worth more than HBJ’s offer, a move that angered HBJ. He alleges that HBJ then seized the land and subjected Al-Attiya to “increasing harassment, threats, and surveillance”. A decade later in 2007, HBJ allegedly tried to have Al-Attiya arrested in Dubai. Al-Attiya then moved to Saudi Arabia in 2008 when a series of legal cases were filed against him, including one that alleged that he leaked state secrets during his tenure serving in public office. Court documents state that Al-Attiya was “forcibly taken from Saudi Arabia to Qatar” in October 2009. From then until January 2011, Al-Attiya was held in various prisons around Qatar. Attiya was told by Qatar’s assistant attorney during this time that “he was being detained at the behest of the prime minister (Hamad bin Jassim), that there was no intention to release him and that any attempt to secure release through securing a court order…would either be prevented or any such order would not be carried out”. Attiya was ultimately released on orders of the crown Prince.

In November 2010 he launched the Humanitarian Appeal 2011 in Doha, together with the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) and the United Nations High Commissioner for Refugees (UNHCR). The initiative is set to help improve the living conditions for millions of people affected by humanitarian crises around the world.

On 25 June 2013, Hamad bin Khalifa al Thani abdicated as Emir of Qatar, and on the next day, 26 June, Hamad resigned from office. Some have questioned whether this was because the new emir pulled him from his post after realizing how much power HBJ had amassed. He was replaced by Abdullah bin Nasser bin Khalifa al Thani as prime minister and by Khalid bin Mohammad al Attiyah as foreign minister. On 3 July, Hamad was also relieved from the post of deputy head of the Qatar Investment Authority (QIA). HBJ’s involvement in so many positions and organizations in Qatar led to questions over his capability to address Qatar’s issues with extremism and terrorist financing, a concern for many western nations who deal with Qatar.

In June 2014, HBJ acquired 80% of Heritage Oil, which was listed as a London exploration and production company. At the same time, he was listed as a “Counsellor” at the Qatari embassy and as such was privileged to legal immunity under the 1961 Vienna Convention. Article 42 of this convention states that “a diplomat shall not in the receiving State practise for personal profit any professional or commercial activity” thereby disallowing the acquisition in which HBJ engaged. The stake, valued at £924 million and dated April 30, 2014, transferred to a “wholly owned subsidiary” of Al-Mirqab Capital, an investment company privately owned by HBJ and his family. HBJ’s lawyers maintain that the fact that the company was listed in London is not sufficient evidence to determine that Article 42 had been violated.

In May 2015, Hamad purchased Picasso's Les Femmes d'Alger (Version O) for $179.4 million including fees, a record price for a painting at auction.

In November 2016, Pakistani Prime Minister produced a letter from Hamad Bin Jassim to claim that the properties identified as owned by his daughter in Panama Leaks are actually are result of a settlement that happened in 2006. The letter was mostly based on hearsay and soon after the first letter second letter was produced which tried to cover up holes left in the first letter. The properties were purchased by Sharif family from 1992–1996 through off shore companies Nescoll and Nielson. The beneficial owner of those four flats is Maryam Safdar (daughter of Prime Minister Nawaz Sharif) according to leaked Panama papers. If the court calls Hamad Bin Jassim to stand as the witness to prove the worth of his letter, he could be sent to prison for lying. Pakistan will definitely imprison frauds who could help making black money white. It is alleged that Hamad bin Jassim's companies got lucarative LNG deal worth Billions of dollar with Pakistan through his connection with Nawaz Sharif. Hammad bin Jasim was even mentioned in Panama case decision and was praised by justice Khosa who used this information to base his opinion and give one of the historical verdicts in Pakistan.

In November 2017 an investigation conducted by the International Consortium of Investigative Journalism cited his name in the list of politicians named in "Paradise Papers" allegations.

HBJ denies all claims against him in regards to Fawaz Al-Attiya and says that he has diplomatic immunity and state immunity given his diplomatic position in London, leaving London’s High Court without jurisdiction. No decision has been made yet as to whether his diplomatic immunity will extend to this case.