Holliday attended the Valdosta Institute,[8] where he received a classical education in rhetoric, grammar, mathematics, history, and languages—principally Latin, but some French and Ancient Greek.

[2]: 50 Holliday moved to St. Louis, Missouri, so he could work as an assistant for his classmate, A. Jameson Fuches, Jr.[2]: 51  Less than four months later, at the end of July, he relocated to Atlanta, where he joined a dental practice.

Allen Barra, an author who focuses on Wyatt Earp, also searched for evidence corroborating the incident and found no credibility in Masterson's story.

During the summer of 1875, he settled in Denver under the alias "Tom Mackey" and found work as a faro dealer for John A. Babb's Theatre Comique at 357 Blake Street.

While dealing cards at John Shanssey's saloon, he met Mary Katharine "Big Nose Kate" Horony, a dance hall woman and occasional prostitute.

Earp left Dodge City, following Rudabaugh over 400 mi (640 km) to Fort Griffin, a frontier town on the Clear Fork of the Brazos River.

In both stories, Holliday was playing cards in the back of the room and upon seeing the commotion, drew his weapon and put his pistol at Morrison's head, forcing him and his men to disarm, rescuing Earp from a bad situation.

Miguel Otero, who would later become governor of New Mexico Territory, said he was present when Holliday walked into the saloon with a cocked revolver in his hand and challenged White to settle an outstanding argument.

Masterson had been asked to prevent an outbreak of guerrilla warfare between the Atchison, Topeka and Santa Fe Railway and the Denver and Rio Grande Western Railroad (D&RGW), which were vying to be the first to claim a right-of-way across the Royal Gorge, one of the few natural routes through the Rockies that crossed the Continental Divide.

[32] Holliday took home a share of a $10,000 bribe paid by the D&RGW to Masterson to give up their possession of the Santa Fe roundhouse and returned to Las Vegas where Horony had remained.

She signed an affidavit implicating Holliday in an attempted robbery and murder of passengers aboard a Kinnear and Company stage coach on March 15, 1881, carrying US$26,000 in silver bullion (equivalent to $821,000 in 2023).

Bob Paul, who had run for Pima County sheriff and was contesting the election he lost due to ballot stuffing, was working as the Wells Fargo shotgun messenger.

[38][39][37] The Earps found witnesses who could attest to Holliday's location elsewhere at the time of the stagecoach murders, and a sober Horony confessed that Behan and Joyce had influenced her to sign a document she did not understand.

He received reports that cowboys with whom they had had repeated confrontations were armed in violation of the city ordinance that required them to deposit their weapons at a saloon or stable soon after arriving in town.

To avoid alarming citizens and lessen tension when disarming the cowboys, Virgil gave the coach gun to Holliday so he could conceal it under his long coat.

In Tucson, on March 20, 1882, the group spotted an armed Frank Stilwell and reportedly Ike Clanton hiding among the railroad cars, apparently lying in wait with the intent to kill Virgil.

On the morning of March 22, a portion of the Earp posse including Wyatt, Warren, Holliday, Sherman McMaster, and "Turkey Creek" Johnson rode about 10 mi (16 km) east to Pete Spence's ranch to a wood cutting camp located off the Chiricahua Road, below the South Pass of the Dragoon Mountains.

[49] Two days later, Earp's posse traveled to Iron Springs, located in the Whetstone Mountains, where they expected to meet Charlie Smith, who was supposed to be bringing $1,000 cash from their supporters in Tombstone.

"[57] On July 14, 1882, Holliday's long-time enemy Johnny Ringo was found dead in a low fork of a large tree in West Turkey Creek Valley near Chiricahua Peak, Arizona Territory.

[60]: 154 [61] A variant of the story, popularized in the movie Tombstone, holds that Holliday stepped in for Earp in response to a gunfight challenge from Ringo, and shot him.

During the trial, "the preponderance of testimony at Holliday’s hearing went to show that Allen was not armed (no gun was ever found), but by then the overriding Western credo of 'no duty to retreat' had won the day with public sentiment.

'No duty to retreat' was a belief, enacted in the laws of several states, that a man who was without blame for provoking a confrontation was not obliged to flee from his assailant but was free to stand his ground regardless of the consequences."

Some modern authors such as Bob Boze Bell[70] speculate that it would have been impossible to transport him to the cemetery, which was only accessible by a difficult mountain road, or to dig a grave because the ground was frozen.

[2]: 410  Tombstone resident George W. Parsons wrote that Holliday confronted Johnny Ringo in January 1882, telling him, "All I want of you is ten paces out in the street."

[42]: 96 No contemporaneous newspaper accounts or legal records offer proof of the many unnamed men whom Holliday is credited with killing in popular folklore.

Tales were told that he had murdered men in different parts of the country; that he had robbed and committed all manner of crimes, and yet when persons were asked how they knew it, they could only admit that it was hearsay and that nothing of the kind could really be traced up to Doc's account.

In addition, Horony denied that Holliday killed "a man named Bailey over a poker game, nor was he arrested and locked up in another hotel room."

She laughed at the idea of "a 116-pound woman, standing off a deputy, ordering him to throw up his hands, disarming him, rescuing her lover, and hustling him to the waiting ponies.

He found evidence to support that Holliday was being held in his hotel room under guard, but for "illegal gambling", and that the story of Horony starting a fire as a diversion to free him was true.

He is typically portrayed in films as being loyal to his friend Wyatt, whom he sticks with during the duo's greatest conflicts, such as the Gunfight at the OK Corral and Earp's vendetta, even with the ensuing violence and hardships that they both endured.