The British actor, who identifies as heterosexual, is currently playing Prior Walter in the critically-acclaimed production at the National Theatre, London.
Asked about his research process, he told a live audience at a discussion (according to Gay Times): “As far as I know, I am not a gay man.
“Maybe I’ll have an awakening later in my life, which I’m sure will be wonderful and I’ll get to explore that part of the garden, but right now I’m secluded to my area, which is wonderful as well.
“I adore it, but a big concern was what right do I have to play this wonderful gay role?”
He added: “I had to trust that it was the right thing and Tony [Kushner, writer] had asked me and maybe if he’d asked me, it was the right thing.
“It was as about doing honour, doing justice and knowing my herstory.
He added: “The preparation had begun before [rehearsals] with a lot of my friends.
“[The play is] as much devoted to my friends in the gay community as it is those that passed during the epidemic.”
Angels In America, which also stars Denise Gough, Russell Tovey and Nathan Lane, has had rave reviews since opening in the spring.
Garfield has had strong reviews across the board, with The Telegraph saying he gives “one of the performances of his career”.
The play runs to August 19.