[5] The inspiration for the screenplay happened one day when he came home from his job to find a dead woman being wheeled out of a drug dealer's apartment across the hall.

Duffy then rented a computer and wrote the screenplay for The Boondock Saints based on his disgust at what he saw: "I decided right there that out of sheer frustration and not being able to afford a psychologist, I was going to write this, think about it.

In March 1997, he was contracted by Paramount Pictures for $500,000, and later in the month, Miramax Films won a bidding war to buy The Boondock Saints.

[11] Duffy also expressed interest in casting Brendan Fraser, Nicky Katt, and Ewan McGregor, with two of them as the brothers, but no decisions were finalized.

The director later sought Patrick Swayze to play the FBI agent, but Miramax preferred Sylvester Stallone (with whom the studio had an existing relationship), Bill Murray or Mike Myers.

After being dropped by Miramax, still believing that the film was a hot commodity, Duffy convinced agents at the William Morris Agency to help him market it to other studios.

The independent studio Franchise Pictures agreed to finance the project, for less than half of Miramax's original budget, once other elements were in place.

After failing to find a distributor at Cannes, the film was eventually picked up by a small company for a limited theatrical release of five theaters in the U.S. for a period of seven days.

Duffy's rise to fame was chronicled in two documentaries: Off the Boulevard (2011), by Jeff Santo, and Overnight (2003), by Tony Montana and Mark Brian Smith.

Through word of mouth, The Boondock Saints has grossed over $50 million in domestic video sales,[16] of which Duffy received nothing due to the structure of the contract he signed with the distribution company.

After a lengthy lawsuit, Troy Duffy, his producers and the principal cast received an undisclosed amount of The Boondock Saints royalties as well as the sequel rights.