Bell was born in Washington Hall, County Durham, England - now known as Dame Margaret Hall - to a wealthy family, which enabled her travel. She is described as having "reddish hair and piercing blue-green eyes, with her mother's bow shaped lips and rounded chin, her father’s oval face and pointed nose". Her personality was characterized by energy, intellect, and a thirst for adventure which shaped her path in life. Her grandfather was Isaac Lowthian Bell, an industrialist, as well as a Liberal Member of Parliament, in Benjamin Disraeli's second term. His role in British policy making exposed Gertrude at a young age to international matters and most likely encouraged her curiosity for the world, and her later involvement in international politics.

Bell's mother, Mary Shield Bell, died in 1871, while giving birth to a son, Maurice. Bell was just three at the time, and the death led to a close relationship with her father. Throughout her life she consulted with him on political matters. Some biographies say the loss of her mother had caused underlying childhood trauma, revealed through periods of depressions and risky behavior. At seven Bell acquired a stepmother, Florence Bell, and eventually, three half-siblings. Florence Bell was a playwright and author of children's stories, as well as the author of a study of Bell factory workers. She instilled concepts of duty and decorum in Gertrude and contributed to her intellectual and feminist activities in the Anti-Suffrage League. Florence Bell's activities with the wives of ironworkers in Eston, near Middlesbrough, may have helped influence Gertrude's later stance promoting education of Iraqi women.

Gertrude Bell received her early education from Queen's College in London and then later at Lady Margaret Hall, Oxford University, at age 17. History was one of the few subjects women were allowed to study, due to the many restrictions imposed on women at the time. Therefore, she specialized in modern history in which she received first class honors degree in two years.

Bell never married. She had an unconsummated affair with Major Charles Doughty-Wylie, a married man and her second love next to Persia, with whom she exchanged love letters from 1913 - 1915. Upon his death in 1915, Bell launched herself into her work.

Bell's uncle, Sir Frank Lascelles, was British minister at Tehran, Persia. In May 1892, after leaving Oxford, Bell travelled to Persia to visit him. She described this journey in her book, Persian Pictures. She spent much of the next decade travelling around the world, mountaineering in Switzerland, and developing a passion for archaeology and languages. She had become fluent in Arabic, Persian, French and German as well as also speaking Italian and Turkish. In 1899, Bell again went to the Middle East. She visited Palestine and Syria that year and in 1900, on a trip from Jerusalem to Damascus, she became acquainted with the Druze living in Jabal al-Druze. She traveled across Arabia six times over the next 12 years. She published her observations in the book Syria: The Desert and the Sown published in 1907. In this book she described, photographed and detailed her trip to Greater Syria's towns and cities like Damascus, Jerusalem, Beirut, Antioch and Alexandretta. Bell's vivid descriptions opened up the Arabian deserts to the western world. In March 1907, Bell journeyed to Turkey and began to work with the archaeologist and New Testament scholar Sir William M. Ramsey. Their excavations were chronicled in A Thousand and One Churches.

In January 1909, she left for Mesopotamia. She visited the Hittite city of Carchemish, mapped and described the ruin of Ukhaidir and finally went to Babylon and Najaf. Back in Carchemish, she consulted with the two archaeologists on site. One of them was T.E. Lawrence. Her 1913 Arabian journey was generally difficult. She was the second foreign woman after Lady Anne Blunt to visit Ha'il.

Bell also became honorary secretary of the British Women's Anti-Suffrage League. Her stated reason for her anti-suffrage stand was that as long as women felt that the kitchen and the bedroom were their only domains, they were truly unprepared to take part in deciding how a nation should be ruled.

At the outbreak of World War I, Bell's request for a Middle East posting was initially denied. She instead volunteered with the Red Cross in France.

Later, from the WWI period until her death she was the only woman holding political power and influence in shaping British imperial policy in the Middle East. She often acquired a team of locals which she directed and led on her expeditions. Throughout her travels Bell established close relations with tribe members across the Middle East. Additionally, being a woman gave her exclusive access to the chambers of wives of tribe leaders, giving her access to other perspectives and functions.

In November 1915, however, she was summoned to Cairo to the nascent Arab Bureau, headed by General Gilbert Clayton. She also again met T.E. Lawrence. At first she did not receive an official position, but, in her first months there, helped Lt. Cmdr. David Hogarth set about organizing and processing her own, Lawrence's and Capt. W.H.I. Shakespear's data about the location and disposition of Arab tribes that could be encouraged to join the British against the Turks. Lawrence and the British used the information in forming alliances with the Arabs.

On 3 March 1916, after hardly a moment's notice, Gen. Clayton sent Bell to Basra, which British forces had captured in November 1914, to advise Chief Political Officer Percy Cox regarding an area she knew better than any other Westerner. She drew maps to help the British army reach Baghdad safely. She became the only female political officer in the British forces and received the title of "Liaison Officer, Correspondent to Cairo" (i.e. to the Arab Bureau where she had been assigned). She was Harry St. John Philby's field controller, and taught him the finer arts of behind-the-scenes political manoeuvering.

When British troops took Baghdad (10 March 1917), Bell was summoned by Cox to Baghdad and given the title of "Oriental Secretary." She, Cox and Lawrence were among a select group of "Orientalists" convened by Winston Churchill to attend a 1921 Conference in Cairo to determine the boundaries of the British mandate and nascent states such as Iraq. Gertrude is supposed to have described Lawrence as being able "to ignite fires in cold rooms". Throughout the conference, the two worked tirelessly to promote the establishment of the countries of Transjordan and Iraq to be presided over by the Kings Abdullah and Faisal, sons of the instigator of the Arab Revolt against Turkey (ca. 1915 - 1916), Hussein bin Ali, Sharif and Emir of Mecca. Until her death in Baghdad, she served in the Iraq British High Commission advisory group there.

Referred to by Iraqis as "al-Khatun" (a Lady of the Court who keeps an open eye and ear for the benefit of the State), she was a confidante of King Faisal of Iraq and helped ease his passage into the role, amongst Iraq's other tribal leaders at the start of his reign. He helped her to found Baghdad's great Iraqi Archaeological Museum from her own modest artifact collection and to establish The British School of Archaeology, Iraq, for the endowment of excavation projects from proceeds in her will. The stress of authoring a prodigious output of books, correspondence, intelligence reports, reference works, white papers; of recurring bronchitis attacks brought on by years of heavy smoking in the company of English and Arab cohorts; of bouts with malaria; and finally, of coping with Baghdad's summer heat all took a toll on her health. Somewhat frail to start with, she became nearly emaciated.

Like Lawrence, Bell had attended Oxford and earned First Class Honours in Modern History. Bell spoke Arabic, Persian, French and German. She was an archaeologist, traveller and photographer in the Middle East before World War I. Under recommendation by renowned archaeologist and historian David Hogarth, first Lawrence, then Bell, were assigned to Army Intelligence Headquarters in Cairo in 1915 for war service. Because both Bell and Lawrence had traveled the desert and established ties with the local tribes and gained unique perspectives of the people and the land prior to WWI, Hogarth realized the value of Lawrence and Bell's expertise. Both Bell and Lawrence stood hardly 5'5", yet both could ride with great determination and endurance through the desert for hours on end. Both died prematurely after recurring bouts of depression, burn-out and exhaustion.

Her work was specially mentioned in the British Parliament, and she was awarded the Order of the British Empire. Some consider the present troubles in Iraq are derived from the lines Bell helped draw to create its borders. Perhaps so, but Gertrude's reports indicate that problems were foreseen, and that it was clearly understood that there were just not many (if any) permanent solutions for calming the divisive forces at work in that part of the world.

As the dismantling of the Ottoman Empire was finalized by the end of the war in late January 1919, Bell was assigned to conduct an analysis of the situation in Mesopotamia. Due to her familiarity and relations with the tribes in the area she had strong ideas about the leadership needed in Iraq. She spent the next ten months writing what was later considered a masterful official report, "Self Determination in Mesopotamia". A.T. Wilson had different ideas of how Iraq should be run, preferring an Arab government to be under the influence of British officials who would retain real control.

On 11 October 1920, Percy Cox returned to Baghdad and asked her to continue as Oriental Secretary, acting as liaison with the forthcoming Arab government. Gertrude Bell essentially played the role of mediator between the Arab government and British officials. Bell had to often mediate between the various groups of Iraq including a majority population of Shi’is in the southern region, Sunnis in central Iraq, and the Kurds, mostly in the northern region, who wished to be autonomous. Keeping these groups united was essential for political balance in Iraq and for British imperial interests. Iraq not only contained valuable resources in oil but would act as a buffer zone, with the help of Kurds in the north as a standing army in the region to protect against Turkey, Persia (Iran), and Syria. British officials in London, especially Churchill, were highly concerned to cut heavy costs in the colonies, including the cost of squashing tribal infighting. Another important project for both the British and new Iraqi rulers was creating a new identity for these people so that they would identify themselves as one nation.

British officials quickly realized that their strategies in governing were adding to costs. Iraq would be cheaper as a self-governing state. The Cairo Conference of 1921 was held to determine the political and geographic structure of what would become Iraq and the modern Middle East. Significant input was given by Gertrude Bell in these discussions thus she was an essential part of its creation. At the Cairo Conference Bell and Lawrence highly recommended Faisal bin Hussein, (the son of Hussein, Sherif of Mecca), former commander of the Arab forces that helped the British during the war and entered Damascus at the culmination of the Arab Revolt. He had been recently deposed by France as King of Syria, and British officials at the Cairo Conference decided to make him the first king of Iraq. They believed that due to his lineage as a Hashemite and his diplomatic skills he would be respected and have the ability to unite the various groups in the country. Shi'as would respect him because of his lineage from Prophet Muhammad. Sunnis, including Kurds, would follow him because he was Sunni from a respected family. Keeping all the groups under control in Iraq was essential to balance the political and economic interests of the British.

Upon Faisal's arrival in 1921, Bell advised him in local questions, including matters involving tribal geography and local business. She also supervised the selection of appointees for cabinet and other leadership posts in the new government. Throughout the early 1920s Bell was an integral part of the administration of Iraq. The new Hashemite monarchy used the Sharifian flag, which consisted of a black stripe representing the Abbasid caliphate, green stripe representing the Ummayad caliphate, and a white stripe for the Fatimid Dynasty, and lastly a red triangle to set across the three bands symbolizing Islam, Bell felt it essential to customize it for Iraq by adding a gold star to the design. Faisal was crowned king of Iraq on 23 August 1921, but he was not completely welcomed. Utilizing Shi'ite history to gain support for Faisal, during the holy month of Muharram, Bell compared Faysal's arrival in Baghdad to Huysan, grandson of Prophet Muhammad. However working with the new king was not easy: "You may rely upon one thing — I'll never engage in creating kings again; it's too great a strain."

In November 1919, Bell was an invited speaker at a meeting for the promotion of a public library in Baghdad, and subsequently served on its Library Committee, as President from 1921 to 1924. The Baghdad Peace Library (Maktabat al-Salam) was a private, subscription library, but in c.1924 was taken over by the Ministry of Education and became known as the Baghdad Public Library (or sometimes as the General Library). In 1961, this became the National Library of Iraq.

Gertrude Bell's first love had always been archaeology, thus she began forming what would later become the Baghdad Archaeological Museum. Her goal was to preserve Iraqi culture and history which included the important relics of Mesopotamian civilizations, and keep them in their country of origin. She also supervised excavations and examined finds and artifacts. She brought in extensive collections, such as from the Babylonian Empire. The museum was officially opened in June 1926, shortly before Bell's death.

Bell briefly returned to Britain in 1925, and found herself facing family problems and ill health. Her family's fortune had begun to decline due to the onset of post-WWI worker strikes in Britain and economic depression in Europe. She returned to Baghdad and soon developed pleurisy. When she recovered, she heard that her younger brother Hugo had died of typhoid. On 12 July 1926, Bell was discovered dead, of an apparent overdose of sleeping pills. There is much debate on her death, but it is unknown whether the overdose was an intentional suicide or accidental since she had asked her maid to wake her.

She never married or had children. Some say the death of Major Charles Doughty-Wylie affected her for the rest of her life and may have added to a depressive state. She was buried at the British cemetery in Baghdad's Bab al-Sharji district. Her funeral was a major event, attended by large numbers of people including her colleagues, British officials and the King of Iraq. It was said King Faisal watched the procession from his private balcony as they carried her coffin to the cemetery.

An obituary written by her peer David G. Hogarth expressed the respect British officials held for her. Hogarth honored her by saying, "No woman in recent time has combined her qualities – her taste for arduous and dangerous adventure with her scientific interest and knowledge, her competence in archaeology and art, her distinguished literary gift, her sympathy for all sorts and condition of men, her political insight and appreciation of human values, her masculine vigor, hard common sense and practical efficiency – all tempered by feminine charm and a most romantic sprit."

In 1927, a year after her death, her stepmother Dame Florence Bell, published two volumes of Bell's collected correspondence written during the 20 years preceding World War I.