He and partner Johnny Irving were longtime members of the Dutch Mob along with Little Freddie and Michael "Sheeny Mike" Kurtz.

He was present during the 1883 gunfight at Shang Draper's saloon in which Irving was shot and killed by rival John "Johnny the Mick" Walsh.

[2]By the mid-1870s, he and partner Johnny Irving became members of the Dutch Mob, a major Manhattan pickpocketing gang, which operated east of The Bowery between Houston and Fifth Streets.

On October 11, 1877, he was arrested with Irving, Joe Dollard and George Leonidas Leslie for stealing $2,000 worth of silk hat linings from E. Tilges' warehouse on Broome Street.

[2] O'Brien was again arrested with Irving on June 5, 1878, and transported to authorities in Brooklyn where they were wanted for the burglary of Mr. Betterman's dry goods store in Williamsburg in which $5,000 worth of silk and $1,400 in cash were stolen.

O'Brien was charged with the burglary of Martin Ibert's Sons' flour and grain store on Graham Avenue which had occurred the previous day.

He was tried twice for the burglary, both trials ending in a hung jury, and he finally escaped with Irving from Raymond Street jail on June 1, 1879.

On July 23, he and Irving also escaped from police in Passaic, New Jersey but O'Brien was eventually apprehended in New York on September 28, and delivered to Sheriff Reilly in Brooklyn.

[2][6] Almost a year after the trial, O'Brien and Irving, then running the so-called Pachen Avenue Gang in Brooklyn, were among those suspected in the unsolved murder of George Leslie, which had occurred back in the summer of 1878.

They had considerable success committing burglaries in England, France and Germany, netting them each $25,000 each, before returning to the United States in January 1885.

He was taken back to Troy to stand trial and it was expected that, were O'Brien not convicted, he would be tried in a separate robbery in Brooklyn where he was suspected of robbing Haydn's jewelry store a year before.