Courtesy HBODavid Oyelowo plays a psychologically twisted young man in HBO’s thriler, “Nightingale,” premiering Friday.

SANTA MONICA, Calif. — When he decided to become an actor, David Oyelowo enlisted two co-conspirators. The man who played Martin Luther King in “Selma” and costarred in “The Help,” “The Butler” and TV’s “MI-5” sneaked into drama school with the help of his teacher.

“I had a great teacher who just said, ‘I wouldn’t say this to everyone because it’s a precarious profession, but I really think you can make a living doing this.’ So she helped me secretly apply to drama school because my Nigerian parents at that time were not partial to the idea of going into anything to do with the arts,” he says in his genteel English accent.

“They’re far more academically minded. But I got a scholarship to go to the London Academy of Music and Dramatic Arts.”

The other ally in his corner was God. “At the age of 16 I became a Christian,” he confides. “My parents were (Christians) but actually I ran in a different direction. Because my parents were, I was like, ‘This is a load of BS. What am I doing in church?’ I made a mistake of striking a deal with God. I said, ‘If you’re real, you need to turn up for me in three months. And if you don’t, I’m out.’”

Evidently God seized the challenge. “I had a very, very dramatic spiritual experience where God infiltrated in my life in a way that I couldn’t deny,” says Oyelowo (who pronounces his name oh-yeh-lo-wo.)

“I heard a voice I hadn’t heard before saying, ‘There’s nothing you can do to make me love you less.’ That floored me because, for me, religion was conditional. If I’m good, then God will like me, and I will go to heaven. But the fact that there was a discernable voice saying to me, ‘No, it’s not about what you do, it’s about who I am in relation to you and how much I want to be in your life.’ So my life was never the same beyond that moment.”

That encounter is difficult to explain, he says. “To talk about God speaking to you is a bit like trying to tell someone what it’s like to fall in love. You know it when you feel it. It’s a very real thing for you, but it’s almost impossible to articulate to someone else unless they’ve felt it themselves, unless they know what that is.”

For 23 years, Oyelowo, 39, has never wavered, either in his calling or his faith. Though he’s occasionally taught acting, he’s never held a job outside the field of acting since he began.

He says he never frets over the roles he chooses, though they can be risky. The most daring so far is his role as the psychologically twisted young man in “Nightingale,” premiering on HBO on Friday. It’s a tour-de-force part in which Oyelowo is the only character in a shuddering thriller.

“Some of the most scary things I’ve ever done have had to do with acting,” he says, nodding. “To play in this film is a very scary thing. To be the only actor in a film for 90 minutes and to try to express the emotional truth of that is very exposing. And if you fail, you fail alone. At least if it’s a group of actors then, ‘OK, we tried.’ With this, it’s me and me and me and me.”

Sighing, he adds, “There’s a world in which you see that opportunity and that reality, and you walk away from it because you don’t want to cut your career short. Actors generally are all on varying scales of knowing that one day they’re going to get found out. I think I have ability as an actor, but you never know.”

His role in “Nightingale” leaves little doubt. But when he and his wife of 16 years, Jessica, decided to pull up stakes and move to the United States, he didn’t work for 14 months and was wracked with doubt.

Ironically it was a film that was never released that turned the tide. He played Muddy Waters in a movie called “Who Do You Love?” And though no one ever saw it, it’s part of his audition tape. When producers observed a sophisticated Brit with an upper-class English accent playing a blues singer from Mississippi, “It’s not who they saw walk in,” Oyelowo says with a smile.

While he relishes his work, it’s not his raison d’être. The father of four children, Oyelowo says his family guides and sustains him. “I saw my first-born son. I remember it so vividly. After he was born, Jess and I came home and put him in his cot. It was a tiny cot, but he only inhabited a tiny corner of it. We were babies ourselves. And I remember us standing there and I was thinking, ‘Oh, my goodness! I am responsible for that little life.’ It gave me the greatest gift as an actor because it was the point beyond which I never looked inwardly anymore. I constantly had someone else on my mind. He gave me the gift of selflessness.”

“Nightingale” also airs on Sunday and June 2, 4, 6, 9, 15 and 17.