Mirabeau Buonaparte Lamar (August 16, 1798 – December 19, 1859) was an American attorney, politician, poet, and leading political figure during the Texas Republic era. He was elected as the second president of the Republic of Texas after Sam Houston. He was known for waging war against bands of Cherokee and Comanche peoples to push them out of Texas, and for establishing a fund to support public education.

Lamar was born in 1798 in Louisville, Georgia, then capitol of the state, as the second eldest of nine siblings, growing up at Fairfield, his father's cotton plantation near Milledgeville, then the later state capital. His family was descended from French Huguenot Thomas Lamar, who had settled in Maryland in 1660. His parents, John and Rebecca (Lamar) Lamar, who were first cousins through Thomas' sons John and Thomas, had allowed his mother's brother Zachariah to name their sons; he named them after his favorite historical heroes. The elder brother, Lucius, was named for the Roman statesman Lucius Quinctius Cincinnatus; the younger, Mirabeau Buonaparte Lamar, for French heroes Napoleon Bonaparte and Honoré Gabriel Riqueti, comte de Mirabeau. The family had connections with other families throughout Georgia and the South. Confederate politician John Basil Lamar was a first cousin to Lamar. As a child, Lamar loved to read. Although he was accepted to Princeton University (then called the College of New Jersey), he chose not to attend. He started work as a merchant and then ran a newspaper, but both of those enterprises failed. In 1823, Lamar's family connections helped him to gain a position as the private secretary to the newly elected Georgia Governor George M. Troup. In this position, Lamar issued press releases and toured the state, giving speeches on behalf of the governor. On one of his trips, he met Tabitha Burwell Jordan, whom he married in 1826. They had a daughter together.

When Troup lost his re-election bid in 1828, Lamar moved with his family to Columbus, Georgia, where he established the Columbus Enquirer. This venture was much more successful than his previous business attempts. In 1830, his wife Tabitha died of tuberculosis. Lamar was deeply affected and took time to recover his drive. He withdrew his name from consideration for re-election to the Georgia Senate, in which he had served one term.

After traveling, Lamar began to study law. He was admitted to the bar in 1833 and ran an unsuccessful campaign for a seat in the U.S. Congress.

Lamar's brother Lucius committed suicide in 1834. A grief-stricken Lamar began traveling again to ease his sorrow. In the summer of 1835, he reached Texas, then part of Mexico. He decided to stay, where he was visiting his friend James Fannin. Fannin had recently settled there and was working as a slave trader in Velasco.

After a trip back to Georgia, Lamar returned to Texas. Learning of a battle for independence, he traveled with his horse and sword to join Sam Houston's army in spring 1836, and distinguished himself with bravery at the Battle of San Jacinto. On the eve of the battle, Lamar courageously rescued two surrounded Texians, an act that drew a salute from the Mexican lines. One of those rescued was Thomas Jefferson Rusk, later appointed as Texas Secretary of War. Lamar was promoted that night from private to colonel and given command of the cavalry during the battle the following day.

Houston noted in his battle report: "Our cavalry, 61 in number, commanded by Mirabeau B. Lamar, (whose gallant and daring conduct on the previous day, had attracted the admiration of his comrades and called him to that station), placed on our right, completed our line."

After Texas achieved independence from Mexico, Lamar was appointed as the Secretary of War in the interim Texian government. In 1836, he was elected to the position of Vice President of Texas.