Jessie Mueller says she was numb with terror to take on her latest role. That’s surprising because she has been performing for more than a decade and has a Tony Award.

But the role was no ordinary one. Mueller is playing legendary country music star Loretta Lynn in the Lifetime feature movie “Patsy & Loretta,” premiering Oct. 19.

The biopic tells of the friendship between successful country singer Patsy Cline and coal miner’s daughter Loretta Lynn.

“Playing a real person, then playing a legend, then a musical icon — so there was all of that,” Mueller said. “And on top of that, there were the technical aspects. I like rehearsal. I like research. I love that stuff, thrive on it.

“And I was one of the later people to get involved in the project, so I was — just on a technical level — ‘Will I have time to do this? Will I learn it? Will I be able to learn the guitar stuff? Will I get on top of the singing stuff that I feel confident about and the interpretation of the songs and get to know her music and her vocal stylings?’

“I was really concerned about the accent,” she added. “And I was nervous about not having enough experience in film and television. Truly I feel like God carried me through.”

Mueller, 36, comes from an acting family. Both her parents are actors, as are her three siblings.

“I guess I thought at a very early age, kind of like 4 or 5, I thought, ‘Wow, if I could do that, maybe that would be really cool and that would be a good thing to invest in.’ So I started going to the theater when I was really tiny. I think that amount of crazy that I think any artist kind of has, it’s a really interesting life,” she said.

“It’s always changing. It doesn’t have a lot of consistency. It doesn’t always have a lot of structure. Sometimes it has a lot of structure and a lot of consistency, and you go through a period of that, and then you have a period of the exact opposite. I find that the most challenging part of it.”

It was during her last two years of high school that she really measured her love for performing against her more practical side. But her mother encouraged her to take the antic leap while she was young and adventurous.

That “adventure” took her to New York, where she slept on an air mattress in a friend’s pad and lived on peanut butter and apples.

She said with a grin, “I’m a Midwestern girl, came from Chicago — maybe I’ll always feel 100 people want your job and it’s always the balance of: I’m unique and I’m just like everybody else. I just want to get the work done, not all that interested in all the stuff that circulates around it. I just like the work.”

Most of her efforts have been in the theater, so plunging into Hollywood and TV stardom is a new and sometimes daunting experience, she said. An avowed perfectionist, Mueller said one of the things that helps keep her grounded is her sweetheart of almost 10 years, Andy Truschinski.

They met in the Chicago production of “A Christmas Carol” at the Goodman Theater. He played the young Scrooge and she was his love interest. “He’s a writer, director and producer, but he’s got the best heart I’ve ever come across,” she quickly added.

“I kind of feel like we are married. He’s stuck with me. Our lives have changed a lot from the time we moved to New York City. He’s stuck by me and held me up at times. I’m very grateful to have people in my life who just know you for who you are.”