Agustín Cosme Damian de Iturbide y Arámburu was born in what was called Valladolid, now Morelia, the state capital of Michoacán, on 27 September 1783. He was baptized with the names of Saints Cosmas and Damian at the cathedral. The fifth child born to his parents, he was the only male to survive and eventually became head of the family. Iturbide's parents were part of the privileged class of Valladolid, owning farmland such as the haciendas of Apeo and Guaracha as well as lands in nearby Quirio. Iturbide's father, Joaquín de Iturbide, came from a family of the Basque gentry who were confirmed in nobility by King Juan II of Aragon. One of his ancestors, Martín de Iturbide, was designated as Royal Merino in the High Valley of Baztan in the 1430s, and thereafter many in the family held political or administrative positions in the Basque Country from the 15th century. As a younger son, Joaquín was not in line to inherit the family lands, so he migrated to New Spain to make his fortune there. While the aristocratic and Spanish lineage of Agustin's father was not in doubt, his mother's ancestry was less clear.

Agustín was married on 27 February 1805 to Ana María Josefa Ramona de Huarte y Muñiz (1786–1861); they had 10 children:

In his teens, Iturbide entered the royalist army, having been accepted as a criollo. He was commissioned as a second lieutenant in the provincial regiment. In 1806, he was promoted to full lieutenant.

He quickly grew in popularity amongst the royalists, whilst becoming a feared foe for the Insurgents. A peerless horseman and a valiant dragoon who acquired a reputation for achieving victory against numerical odds, his prowess in the field gained him the nom de guerre of "El Dragón de Hierro" or "The Iron Dragon", in reference to his skill and position in the army. He was given an important charge in the army, however he was accused by locals of using his authority for financial gain, although he was recognized as valiant in combat. These accusations were unable to be proved, though they did cost him his charge. He turned down the offer to reclaim his post since he felt his honor had been damaged. He may have been involved in the initial conspiracy to declare independence in 1809 that was headed by José Mariano Michelena in Valladolid. It is known, by his and Hidalgo's documents, that he was a distant relative of Miguel Hidalgo, initial leader of the Insurgent Army. Hidalgo wrote to Iturbide, offering him a higher rank in his army. Iturbide writes in his memoirs that such an offering required musing over it, but that he ultimately turned it down because he considered Hidalgo's uprising ill-executed and his methods barbaric.

From 1810 to 1820, Iturbide had fought against those who sought to overturn the Spanish monarchy and Bourbon dynasty's right to rule New Spain and replace that regime with an independent government. In this, he was solidly aligned with the Creole class. However, events in Spain caused problems for this class, as the very monarchy they were fighting for was in serious trouble. The 1812 Cadiz Constitution, that was reinstated in Spain in 1820 after the successful Riego Revolt, established a constitutional monarchy, which greatly limited Ferdinand VII's powers. There was serious concern in Mexico that the Bourbons would be forced to abandon Spain altogether. This led to the disintegration of viceregal authority in Mexico City and a political vacuum developed that the Mexican nobility sought to fill, seeking limited representation and autonomy for themselves within the empire. An idea arose among this class that if Mexico became independent or autonomous, and if Ferdinand were deposed, he could become king of Mexico.

Both the sitting viceroy and Fernando VII rejected the Plan of Iguala. The Spanish parliament sent a new "viceroy", Juan O'Donojú, to Mexico. (Technically, the office of viceroy had been replaced by a "superior political chief" under the 1812 Spanish Constitution.) O'Donojú however, arrived to witness a nation on the brink of achieving Independence and knew its consummation could not be stopped.

As a captain, he pursued rebel forces in the area, managing to capture Albino Licéaga y Rayón, leading to another promotion. In 1813, Viceroy Félix María Calleja promoted Iturbide to colonel and put him in charge of the regiment in Celaya. Then, in 1814, he was named the commander of forces in the Bajío area of Guanajuato where he continued to pursue rebels with vigor, in a strongly contested area, and was Morelos’ principal military opponent from 1813 to 1815.

Iturbide's persistence against the rebels was widely known as well as his views against their liberal, anti-monarchical politics. In his diary, he refers to the insurgents as "perverse," "bandits," and "sacrilegious." In a letter to the viceroy in 1814, he wrote of how he had 300 rebels (to whom he referred as excommunicates) executed to celebrate Good Friday. Iturbide was also criticized for his arbitrariness and his treatment of civilians, in particular his jailing of the mothers, wives and children of known insurgents. As for corruption, the Count of Pérez Galvez extensively testified that profiteering by many royalist officers, of whom Iturbide was the most visible, was draining the effectiveness of the royal army. Iturbide accrued a large personal fortune before 1816 through questionable dealings. Some of these shady practices included creating commercial monopolies in areas he controlled militarily. Other accusations against Iturbide included sacking private property and embezzling military funds. In 1816, the viceroy relieved Iturbide of his command for corruption and cruelty.

Iturbide was fully reinstated to military command in November 1820 by viceroy Juan Ruiz de Apodaca. He was reinstated as colonel of the royalist army and general of the south of New Spain. For a couple of years after the defeat of Morelos at Puruarán, the independence movement had diminished significantly. However, Iturbide was given the task of putting down the remaining insurrectionist movement southwest of Mexico City led by Vicente Guerrero . Iturbide installed his headquarters at Teloloapan. For more than a century, historians believed that Iturbide had first attempted to carry out his duty in destroying Guerrero, but that he met with failure and so decided to strike an alliance with the rebel. However, in 2006, new evidence was discovered by Mexican Historian Jaime del Arenal Fenochio, namely, a letter between the two military Leaders dated November 20, 1820, which also referenced a previous letter. Since communications have been proven to have existed between the two Leaders before Iturbide ever set out to seek out Guerrero, it is now believed that the two were carrying out negotiations at this time. Regardless, some encounters between the two military forces were unavoidable, as Guerrero and Pedro Ascencio's (another insurgent leader) troops managed to force Iturbide's rear guard to withdraw from an ambush. In their further correspondence, Iturbide and Guerrero lament the clashes and Iturbide attempts to further convince Guerrero of his intentions of liberating Mexico.

This led to political destabilization, which was resolved temporarily when Iturbide was elected Emperor of the Mexican nation. However, it is not clear whether he took this crown at the insistence of the people or whether he simply took advantage of the political situation. Accounts of the time sustain the hypothesis that it truly was the wish of the people that Iturbide, who had gained unparalleled fame thanks to his role in achieving Independence, were crowned Emperor. Some call Iturbide's decision a coup and state that the public support for Itubide was orchestrated by him and his followers. Others insist that the people's offer of the throne was sincere, based on there being no other candidate and the people's gratitude to him for the liberation of Mexico. The latter accounts stress that Iturbide initially rejected the offer in favor of persuading Ferdinand VII to change his mind about ruling Mexico but then reluctantly accepted. It should be noted that when the liberating army entered Mexico on September 27, 1821, the army sought to proclaim Iturbide as Emperor, a proclamation that Iturbide himself stopped, with no lack of effort. A month later, on October 28 he was publicly proclaimed Emperor by the people but again refused any such attempt.

Santa Anna publicly announced his opposition to Iturbide in December 1822 in the Plan of Veracruz, supported by the old Insurgent hero, Guadalupe Victoria. Santa Anna would later admit in his recollections of his life that, at the time, he did not know what a republic was. The Emperor had tried to stop Santa Anna by inviting him to Mexico City. Recognizing the danger of such an invitation, Santa Anna responded with his Plan de Veracruz, which called for the reinstatement of the old Constituent Congress, which would then have the right to decide which form of Government the new nation would acquire. Curiously, it did not specifically call for a Republic, and it did not call for the abdication of Iturbide. Santa Anna wrote Iturbide, explaining his reasons and swearing to sacrifice his own life if necessary to ensure the safety of the Emperor. Iturbide's enemy-turned-ally, Vicente Guerrero, turned to enemy again when he and General Nicolás Bravo escaped México City and allied themselves with the rebels. In a proclamation that explained their reasons, they too called for the reinstatement of the disintegrated Congress, which would then decide the fate of the nation. Bravo and Guerrero wrote that they swore to abide by the Congress' decision, even if it decided to stay as a Constitutional Empire and even if it elected Iturbide again to lead them.

On 11 May 1823, the ex-emperor boarded the British ship Rawlins en route to Livorno, Italy (then part of the Grand Duchy of Tuscany) accompanied by his wife, children, and some servants. There he rented a small country house and began to write his memoirs, known with the name of Manifiesto de Liorna. Iturbide and his family struggled financially during this time, despite claims by historians and some members of the congress that deposed him that Iturbide had indulged in illegal enrichment throughout his military career and rule. In exile, Iturbide was approached by a Catholic Coalition of nations that sought to enlist his help in a campaign to reconquer México for Spain. Iturbide declined. Spain pressured Tuscany to expel Iturbide, and the Iturbide family moved to England. Here, he published his autobiography, Statement of Some of the Principal Events in the Public Life of Agustín de Iturbide. When he was exiled, Iturbide was accorded a government pension, although it was never received by Iturbide. Congress also declared him a traitor and "outside of the law," to be killed if he ever returned to Mexico. Iturbide was unaware of this penalty. After his death, many an author decried the decree calling for Iturbide's death, as it was against all known precepts of the law at the time, for it was unheard of that a law could be issued solely against a specific citizen, instead of issuing a general law which would then be applied to particular cases.

Liberal or republican ideas were and would continue to be embraced by creoles outside the Mexico City elite. These came out of Bourbon reforms in Europe that were based on the Enlightenment. Attacks on the Church by liberals in Spain and elsewhere in Europe would be repeated in Mexico during the La Reforma period. Ideals of the Constitution of Cadiz would find expression in the 1824 Constitution of Mexico. An interesting fact is that this constitution would influence political thought on both sides of the Mexican political spectrum, with even Iturbide bending to it when he created the first congress of an independent Mexico. After Iturbide, there was wide general consensus, even among the landed elite, that some form of representative government was needed. The question was how much power would be in legislative hands and how much in an executive.

His body was buried and abandoned at the parish church of Padilla until 1833. In that year, President Santa Anna decided to rehabilitate the memory of Iturbide, ordering that his remains be transferred to the capital with honors. However, it was not until 1838, during the presidency of Anastasio Bustamante, that this order was confirmed and carried out. His ashes were received in Mexico City with much pomp and ceremony, and the same Congress that had been against him for so many years gave him honor as a primary hero of the War of Independence.

On 27 October 1839, his remains were placed in an urn in the Chapel of San Felipe de Jesús in the Mexico City Cathedral, where they remain. On the stand is an inscription in Spanish that translates to: "AGUSTÍN DE ITURBIDE. AUTHOR OF THE INDEPENDENCE OF MÉXICO. COMPATRIOT, CRY FOR HIM; PASSERBY, ADMIRE HIM. THIS MONUMENT GUARDS THE ASHES OF A HERO. HIS SOUL RESTS IN THE BOSOM OF GOD." Iturbide's remains still rest in the Metropolitan cathedral.

While Iturbide's reign lasted less than a year, it was the result of and further defined the struggle between republican and traditional ideals, not only in Mexico, but also in Europe. For a number of Mexican autonomists, a constitutionally sanctioned monarchy seemed a logical solution to the Problem of creating a new state as it seemed to be a compromise between those who pushed for a representative form of government and those who wished to keep Mexico's monarchist traditions. One must keep in mind that a Republican, Federalist government was virtually unheard of, and that for 300 years New Spain had lived in a monarchy. When things are viewed in this light, Historian Eric Van Young states that Iturbide's seizure of the crown "seems less cynical and idiosyncratic when it comes along at the end of the independence struggle." However, the rest of the 19th century would be marked by oscillation between the two political extremes, with each side gaining the upper hand at one point or another. The old Mexican nobility kept their titles and coats-of-arms close at hand, ready for a comeback. Members of the Iturbide family intrigued against the Mexican government in Madrid, New York City, Paris, and Rome as late as the 1890s.

In 1921, former revolutionary general and newly elected President of Mexico Alvaro Obregón mounted a massive centenary celebration for Mexican independence, even larger than the one that Porfirio Díaz had staged in 1910, and the first time since the mid nineteenth century that the date was commemorated. The 1921 commemoration was an opportunity for Obregón to assert his own state-building vision by appropriating a piece of Mexico's history. By overseeing the ceremonies, Obregón could shape and consolidate his own position in power, which at the time was relatively weak. The Mexican Army benefited from the celebrations with new uniforms and equipment, and there was even a re-enactment of Iturbide's triumphal entry into Mexico City.

This situation did not last long. Soon Iturbide was unable to pay his army, forming discontent in a significant portion of his power base. When criticism of the government grew strong, Iturbide censored the press—an act that backfired against him. Opposition groups began to band together against the Emperor. Leaders such as Valentín Gómez Farías and Antonio López de Santa Anna began to conspire against the imperial concept altogether and became convinced that a republican model was needed to combat despotism.

Iturbide's empire was replaced with the First Republic. Guadalupe Victoria was elected as the first President, but in subsequent years, Vicente Guerrero became the first in a long line of Presidents to gain the Presidency through a military revolt after losing an election. Guerrero was betrayed and assassinated, and Santa Anna would rise to avenge him, beginning the era of Mexican History that Santa Anna so clearly dominated. This regime would oscillate and finally be overcome by the Plan of Ayutla. The new Government would struggle between anti-clerical, reformist views and conservative views during the Reform War. During the French Intervention the country would face Civil War amongst conservative, Catholic, Europe-adherent monarchists led by the ironically liberal Maximilian I of México, and liberal, masonic, anti-clerical, reformist and United States-adherent liberals led by the American-backed Benito Juárez. Having prevailed, Juárez died after 15 years of forcefully remaining as President. Porfirio Díaz in the late 19th century would install a one-man rule which imposed upon México its first true period of relative peace, in exchange for freedom, and Díaz remaining for the next 30 years in power. He would be overthrown with the Mexican Revolution.

In modern-day Mexico, the liberal tendency has dominated, to the extent that the conservative movements are academically and politically almost ignored. When they are treated, it is with a strong partisan slant. This is true of much of the writing about Iturbide, being portrayed as a "traitor" of 19th century Mexico. Many an author, including Timothy E. Anna, consider that a historical injustice has been committed against Iturbide, as his enemies had the privilege of writing history.