Scorsese and actor Robert De Niro started planning the film adaptation of Charles Brandt's book "I Heard You Paint Houses" 12 years ago.
"Things got in the way," Scorsese told journalists Friday after the world premiere screening. "We couldn't get backing -- there was no way -- for years," he added.
"I'm just happy we all got finally to do it because it did take a long time," said De Niro. "We were lucky to get people to put up the money."
After several studios declined the project, it took Netflix's deep pockets to get the green light for "The Irishman" -- the nickname of Frank Sheeran, whose account of real-life events forms the basis of the book and film.
Former henchman Sheeran (played by De Niro) claimed to have killed more than 25 people on the orders of mafia boss Russell Bufalino (Joe Pesci) and truck driver union leader Jimmy Hoffa (Al Pacino).
The film uses a new technology developed by Industrial Light & Magic (ILM) -- the effects firm created by George Lucas -- to digitally "de-age" actors on screen.
De Niro, 76, is able to play Sheeran across several decades, from a 34-year-old in 1955 to his 2003 death aged 83.
Scorsese said it was necessary to "come up with a solution for a de-aging that wouldn't interfere with Bob and Joe and Al."
"Talking to each other with helmets on or tennis balls in their faces -- they were not going to do it," he said.
ILM eventually succeeded in developing technology which did not require fitting the actors with any devices.
After an unsettling first few minutes the special effects work well, with Pacino also shedding multiple decades in some scenes.
De Niro's first reaction to when he saw his younger digital self? "I could extend my career another 30 years," he joked.
Murder and morality
The movie will be released in a limited number of theaters in the United States on November 1, before it appears on Netflix from November 27.
With "The Irishman" Scorsese returns to the gangster movie genre, following "Goodfellas," "Casino" and "The Departed."
But this film adheres more closely to real-life facts and characters.
It also sets a slower, calmer pace than those earlier films, taking a step back as Sheeran, as an old man, takes stock of his life in a series of flashbacks and examines the morality of each event.
The movie also revolves around a key episode of his relationship with Hoffa, in 1975.
"He finds himself at the most important point of his life in a moral conflict because he's basically a good man," said Scorsese.
The director also makes greater use of dialogue, in particular humor, illuminating scenes between acting giants De Niro and Pacino.
Scorsese said he wanted to evoke the atmosphere of the 1960s as a violent time when it seemed like "everybody was getting shot," starting with President John F. Kennedy.
Seemingly tracing a link from those events to the current day, the director described "the true dark forces that are in our nation."
"It doesn't happen maybe with one gunshot," said Scorsese cryptically. "It happens on every level incrementally and before you know it, it's over." —AFP
