McParland first came to national attention when, as an undercover operative using the name James McKenna, he infiltrated and helped to dismantle an organization of activist Pennsylvania coal miners called the Molly Maguires.

McParland turned in reports daily, eventually collecting evidence of murder plots and intrigue, passing this information along to Benjamin Franklin, his Pinkerton manager.

He also began working secretly with Robert Linden, a Pinkerton agent assigned to the Coal and Iron Police for the purpose of coordinating the eventual arrest and prosecution of members of the Molly Maguires.

If I was not here the Vigilante Committee would not know who was guilty and when I find them shooting women in their thirst for blood I hereby tender my resignation to take effect as soon as this message is received.

[11] Eventually enough evidence was collected on reprisal killings and assassinations that arrests could be made and, based primarily on McParland's testimony, ten Molly Maguires were sent to the gallows.

[12]Joseph G. Rayback, author of A History of American Labor, has observed: The charge has been made that the Molly Maguires episode was deliberately manufactured by the coal operators with the express purpose of destroying all vestiges of unionism in the area ...

The evidence brought against [the defendants], supplied by James McParlan, a Pinkerton, and corroborated by men who were granted immunity for their own crimes, was tortuous and contradictory, but the net effect was damning ...

More important, it gave the public the impression ... that miners were by nature criminal in character ...[13]Reports of McParland's success against the Molly Maguires came to the attention of Sir Arthur Conan Doyle, author of the Sherlock Holmes detective fiction.

Conan Doyle had met Allan Pinkerton[clarification needed] on an ocean voyage, where the writer became fascinated by the "singular and terrible narrative" of the Molly Maguires.

[16]During the Knights of Labor Railway Strike of 1886, McParland worked undercover in Parsons, Kansas for railroad tycoon Jay Gould.

Writer Anthony Lukas recorded that: For years, its staff had preyed on visitors – notably Texas cattlemen who, having driven their herds up the Chisholm Trail to Abilene returned through Parsons with bulging pockets.

[18] Lukas wrote: "What lay behind these accusations is difficult to say," and that it is "hard to imagine" how McParland became associated with "a scoundrel like McLaughlin," but "if the story is accurate," he speculated that the connection must have resulted from activities relating to the strike.

McParland tricked Thomas Thatcher Graves, her accused murderer, into traveling from Providence, Rhode Island, to Denver where he was arrested and convicted of the crime.

McParland hired gunman Tom Horn (later executed for murder in Wyoming), who, while working for Pinkerton killed seventeen men, according to a count by Siringo.

Bill Haywood, Secretary Treasurer of the WFM, wrote about the sabotage in his autobiography: I had been having some difficulty with the relief committee of the Denver smelter men.

On December 30, 1905, Steunenberg, five years out of office, opened the side gate of the picket fence at his house in Caldwell, which set off an explosive device that took his life.

"[30] McParland frequently used the expression inner circle to describe a secret cabal in the Western Federation of Miners when pitching Pinkerton's services to mine owners.

McParland allayed Orchard's skepticism by telling him about "Kelly the Bum", a confessed murderer who became a prosecution witness in the Molly Maguires cases.

[40] McParland had Western Federation of Miners leaders Bill Haywood, Charles Moyer, and George Pettibone arrested in Colorado.

In his book Roughneck, writer Peter Carlson wrote that the extradition papers falsely claimed that the three men had been present at Steunenberg's murder.

[44] McParland sought to bolster Orchard's testimony by forcing another WFM miner, Steve Adams, to turn state's evidence.

McParland had contracted to provide Pinkerton services for Bulkeley Wells, the president and manager of the Smuggler-Union Mining Company in Telluride, Colorado.

[49] At the Haywood trial, which was funded, in part, by direct contributions from the Ceour d'Alene District Mine Owners' Association to prosecuting attorneys,[50] the only evidence against the WFM leader was Harry Orchard's testimony.

[54] Orchard had burglarized a railroad depot, rifled a cash register, stolen sheep, and had made plans to kidnap children over a debt.

[55] To satisfy McParland, Orchard had signed a confession to a series of bombings and shootings which had killed at least seventeen men, all of which he blamed on the Western Federation of Miners.

Edward testified that he had been working at his cobbler's bench in Victor when national guardsmen: ... took him in custody, striking him several times with their gun butts for moving too slowly.

After days in a Cripple Creek bullpen, he and seventy-seven others were put on a train and deported to neighboring Kansas ...[62]The appearance of his brother Edward was intended "simply to embarrass" the detective, for it recounted "the imperial style of the Peabody administration in Colorado, with which McParland and the Pinkertons had been closely associated.

[68] When "The Cowboy Detective" Charlie Siringo wrote his memoirs about working for the Pinkerton Agency, he accused McParland of ordering him to commit voter fraud in the re-election attempt of Colorado Governor James Peabody.

[69] Charles A. Siringo, a Pinkerton who had worked for more than twenty years as an operative, detective, and spy, and McParland's personal bodyguard in Idaho, declared the agency "corrupt".

[His 1915 book charged the Pinkertons with election fraud, jury tampering, fabricated confessions, false witnesses, bribery, intimidation, and hiring killers for its clients ...