Beidler, who preferred to be called simply "X," had little formal education and tried his hand at a variety of trades. Initially a shoemaker, he also worked briefly as a brick maker and then traveled to Kansas where he took up farming. A supporter of John Brown's radical abolitionist movement, he left Kansas for Texas after Brown was captured and executed for his abortive raid on the Harper's Ferry armory in Virginia. From Texas, Beidler wandered northward, eventually joining the Gold Rush to Montana Territory in 1863.
When Beidler arrived in Virginia City, the area was plagued by marauding bandits who roamed the isolated roads of the region robbing and killing. The bandits were led by a charming psychopath named Henry Plummer who had managed to con the citizens into electing him sheriff of the nearby town of Bannock. Frustrated by the ineffectiveness of the local law enforcement, the citizens of Virginia City and Bannock formed a highly secretive vigilance committee and began systematically hunting down and hanging the road agents, including Sheriff Plummer.
Not long after arriving in Virginia City, Beidler joined the vigilantes and became one of the group's most active members. Unlike most of the members, who took pains to conceal their identities, Beidler welcomed attention. Numerous legends arose around the so-called "Vigilante X," and Beidler did little to discourage exaggerations—in fact, much of the Beidler lore was true. He was the principal hangman for at least five of the vigilante's victims, and he survived several narrow escapes in his relentless pursuit of dangerous men.
After helping rid Montana of crime, Beidler became a stagecoach guard and deputy U.S. Marshall. He appears to have been highly effective in these roles, though he was criticized for sometimes overstepping the bounds of his authority. Apparently, the former vigilante still liked to take the law into his own hands.
As an old man, he fell on hard times and became dependent on the charity of Montanans who remembered his previous service. When he died in Helena, Montana, in 1890, his death certificate listed his occupation as "Public Benefactor."