Fassbender, 36, recalled the discussion during a recent press conference in New York.
"He was like, 'The next thing I want to do is make a film about slavery,'" the actor quoted McQueen as saying.
"And I was like: 'Of course!' It seemed pretty obvious.
"Steve always seems to tackle the elephant in the room. So that was the first I'd heard of it. And then, several months later, I got a script and I wasn't sure what part Steve had me in mind for. I was hoping it would be Epps, but I called him up as soon as I read the script. By the end of it, I was in tears. I found it such a moving story, such an incredible story. I couldn't believe it was a true story. I never heard anything about it before. So I called him up immediately and said: 'Whatever. If this is one day, two days of work on this job, whatever. I just want to be a part of it.' It felt like it was a really important story to tell. And, luckily enough, he offered me Epps."
Based on Solomon Northup's 1853 memoir, "12 Years a Slave" was written for the screen by John Ridley. Chiwetel Ejiofor plays Northup, a free black man from New York, who is kidnapped in 1841 and ultimately sold to Fassbender's character Edwin Epps, a cruel Louisiana plantation owner whose treatment of his favorite slave Patsey, played by Lupita Nyong'o, incurs the wrath of his insecure wife Mary, played by Sarah Paulson.
Asked how much he knew about American slavery before he began working on the film, Fassbender replied: "History was always an important subject for me, one of my favorite subjects and, in Ireland, we're proud to teach our own history, but international history, also, and so I was always very much aware of American history and the slave trade. ...
"So, I was well-versed in it and when I got the script, the story was told in such an eloquent, complex way," he said. "I was just privileged to be a part of it."
The star of TV's "Hex" and the films "Inglourious Basterds," "X-Men: First Class," "Jane Eyre" and "Prometheus" said he attempted not to judge his odious character in "12 Years a Slave" because he wanted to truly breathe life into the man and portray him the way he would have been more than 150 years ago.
"We're all human beings and all made up of the same thing. There is a lot of fear in these characters and they're tortured," Fassbender observed. "We're human beings and what was happening on the Epps plantation was affecting everybody. Of course, [for] the oppressed [it] is a terrible place. It was a living hell what the slaves went through, but the oppressors, also. There is a transference of that pain. To be giving out that pain to somebody every day and to be living in this abnormal way, which is normality, it has an effect on everyone. So for me, it was important to -- if it's just a glimpse or a second for the audience when they see Epps at any certain time and they're like, 'God, I recognize something in myself there.' That was the object for me in bringing Epps to the screen. That it wasn't a guy that the audience could very easily hold at an arm's length away from themselves and go: 'Well, that's him. I would never be like that.' I wanted to try to have some sort of an empathy as an audience member looking at him so it is harder to deal with because you're like, 'There is something I recognize there or somebody that I know I recognize.' Make human beings out of them as opposed to keeping them at a safe distance from all of us, including myself."
Co-starring Benedict Cumberbatch, Paul Dano, Alfre Woodard, Paul Giamatti and Brad Pitt, "12 Years a Slave" is in theaters now. It is nominated for nine Oscars, including Best Picture. Ejiofor is up for Best Actor, while N'yongo and Fassbender are nominated for Best Supporting Actress and Actor, and McQueen for Best Director.