Born in Nashville, Tennessee, he graduated summa cum laude from University at the early age of fourteen; he then went on to qualify as both a doctor and a lawyer. He also edited a newspaper in New Orleans and later, California.
On October 15, 1853 with just forty-five men he set out on his first filibustering expedition, the conquest of the Mexico province of Baja California. However, lack of supplies and unexpected resistance by the Mexican government forced him to abandon the enterprise.
Invited by Nicaraguan rebels a year later, Walker invaded Nicaragua with 56 or 58 men. He managed to gain control of the country and was elected as its president. On May 20, 1856 Walker's government was formally recognized by U.S. President Franklin Pierce. However Nicaragua was invaded by a coalition of other Central American states led by Costa Rica and financed by Cornelius Vanderbilt who had had a cozy relationship with the previous regime. Vanderbilt was at odds with Walker because he had nationalized his Transit Route through Nicaragua. A year later in May 1857 Walker was driven from the country. He surrendered to the United States Navy and was repatriated.
Within six months he was off on another expedition but was arrested by the US Navy soon after landing at Punta Arenas and once again returned to the States. Over the next four years he made several more attempts to return to Nicaragua.
Finally in 1860 he invaded Honduras. However, he was soon in the custody of Captain Salmon of the British Navy. Rather than returning him to the United States, Captain Salmon handed him over to the Honduran authorities along with his fellow conspirators. They were all executed by firing squad on September 12, 1860.
Walker has inspired the subject of two films, both taking considerable liberties with his story: "Burn!" (1969) starring Marlon Brando and "Walker" (1987) starring Ed Harris. Walker's name is used for a character in the film "Burn!" but it is not meant to be the actual historical figure.
William Walker should not be confused with David Walker, who was also alive during the 1820s. He should also not be confused with the British ambassador to Nicaragua also named William Walker.