Jonathan Groff, center, as Craig in ‘The Normal Heart.’ (Photo by Jojo Whilden, courtesy HBO)

When director Ryan Murphy and writer Larry Kramer (both out) announced they were adapting Kramer’s groundbreaking and Tony-winning play “The Normal Heart” for HBO, a virtual who’s who of stars clamored to take part in the powerful and emotional story that deals with the onset of the AIDS crisis in New York City in the early 1980s.

The cast quickly filled with respected names like Julia Roberts, Mark Ruffalo, Jim Parsons, Taylor Kitsch and Matt Bomer.

“The Normal Heart” follows Ned Weeks (Ruffalo), a gay activist enraged at the indifference of public officials and the gay community. Bomer plays a reporter who becomes Ned’s lover; former “Friday Night Lights” star Kitsch plays Bruce, a closeted investment banker who becomes a prominent AIDS activist; Roberts plays Dr. Emma Brookner, who treats some of the earliest victims of the epidemic; and Parsons portrays gay activist Tommy Boatwright, reprising his critically praised Broadway role.

One actor who was dreaming of taking part was Jonathan Groff. Although too young to remember the events of the time, the 29-year-old had seen the play during its Off-Broadway revival in 2004 and again when it opened on Broadway in 2011.

“I had seen it several times and it’s such an important piece of writing and it means so much,” Groff says. “When I learned HBO would be turning it into a film, something that would last forever, I wanted to be part of it.”

Luckily, Groff already had a relationship with Murphy, having worked with him on “Glee,” playing the one-time Vocal Adrenaline powerhouse Jesse St. James.

“Ryan texted me and said he had this part for me in the movie, and I called him back right away and said, ‘Absolutely, I would do anything in this movie because it’s such a special project,’” Groff recalls. “I feel very lucky to be in it.”

In the movie, Groff plays Craig Donner, a character barely mentioned in the play, but one who has an extremely important role in the film. He plays the boyfriend of Bruce and ex-boyfriend of Ned.

“Craig is based on one of Larry’s friends from Fire Island, when the ‘gay cancer’ at the time started hitting this circle of friends, and Craig was the first one to go,” Groff says. “It hit him so quickly that when he died, his body was still tan. It was horrifying.”

For the part, Groff worked on location at Fire Island, shooting some of the earliest scenes of the movie.

“We did a bunch of the boys partying it up on Fire Island,” he says. “It was nice to be at the beginning of the movie. We were all having a blast, and then it got pretty dark.”

With longtime friend Lea Michele by his side, Groff joined the cast for an opening night screening last week at New York City’s Ziegfeld Theater and said it was unlike any movie premiere he had ever attended.

“Here we are at the Ziegfeld with the whole cast and crew and a lot of the men and women who lived through the AIDS crisis in New York City at the time and watching it in that venue was just incredibly powerful and a night I will never forget,” he says. “Everyone in that room felt so personally connected to the story we were telling. It is such an amazing movie and has such an effect on people — some had to walk out because it was so much. When we left the theater, there was that same sadness and reverence you have when you leave a funeral, it was a really powerful experience.”

Groff admits that the movie is a little different from the play, but that it almost had to be to pull off its importance on screen.

“Ryan is so visual, so he creates some amazing pictures and the way he pulls the story together has the spirit of the play and a lot of those same lines and speeches that we love, but there’s something very specifically Ryan Murphy about the movie that makes the sensibility a little different,” he says. “It’s the same overall experience, but you are served it in a different way.”

“The Normal Heart” debuts on HBO at 9 p.m. Sunday and is expected to be seen by millions, a far greater reach than the play ever could secure.

“When it’s on a network like HBO that everyone looks to as the benchmark of quality programing, you get a lot of people paying attention to what they put out,” Groff says. “We have Taylor and Julia and Matt and Mark, and hopefully it adds a lot of eyes to the story of those who wouldn’t have watched it before and that reach grows once the movie starts to air.”

In addition to being part of this landmark movie, Groff has had a pretty exciting year already. He starred in HBO’s new series, “Looking,” which will be returning for season two this fall and voiced Kristoff in Disney’s mega-hit “Frozen.”

“The movie exploded in ways that I don’t think anyone who worked on it thought it would, certainly we all thought it was great, but you can never predict a phenomenon,” he says. “I feel extremely lucky to be a part of this history.”

For those who know him from his Tony-nominated role of Melchior Gabor in “Spring Awakening” or one of the many other theatrical productions he’s done, Groff says he is itching to get back to the Great White Way.

“I rented an apartment in New York a couple of weeks ago and I spent every night last week watching plays. I am a theater nerd and a fan and I try to see everything and I want to be back on that stage. It’s just hard to find the time and find the right project, but it’s something I definitely hope to be doing soon.”

Born in 1985, Groff feels he is part of “a younger gay generation” whose members don’t always understand the history of those who came before. He hopes the movie will change the way that some approach their advocacy efforts.

“I think there’s a disconnectedness that my generation has in some ways for the AIDS crisis and what the generation before us went thought emotionally but fought for and got political and advocated about,” he says. “I hope probably more than anything that the movie reaches my generation and not only teaches us about what happened before us, but inspires us to advocate and stay connected to each other and protect each other and continue to be vocal.”