Keira Knightley was tired of being depressed and ill. On screen, at least.

The Oscar-nominated actress spent five years playing a series of heavy roles — from a young woman harvested for her organs in “Never Let Me Go” to a love-struck Russian aristocrat who has an unfortunate encounter with a train in “Anna Karenina.”

“It had all been very, very dark with very little hope and I wanted to find something with hope in it where I didn’t die in the end,” Knightley told Variety at Wednesday’s New York premiere of “Begin Again.”

The film, an uplifting story about a young woman and a washed-out record producer who help each other rebound from a series of personal setbacks, was the perfect antidote.

“Romantic comedies aren’t normally a genre I go for, but I read this one and thought it actually makes me feel good,” said Knightley. “It actually makes me feel hopeful without making me feel like I’m being drowned in sugar.”

PHOTOS: More from the “Begin Again” premiere + More of This Week’s Parties

The film pairs Knightley, the cinematic embodiment of poshness, with Mark Ruffalo, as a down and out music producer so hard on his luck audiences can practically touch the stubble and smell the cheap booze. Director John Carney (“Once”) said he was inspired to put the two actors together on screen because of their radically different personas.

“It was a little bit ‘Guys and Dolls’-ish,” said Carney.  “A little bit Marlon Brando and Jean Simmons. They had a transatlantic sort of chemistry.”

“Begin Again” inspired a bidding war when it debuted at last year’s Toronto Film Festival, with the Weinstein Co. emerging as the winner.  At the premiere, the studio’s chief Harvey Weinstein told the audience inside the SVA Theatre that he fell in love with the picture in large part because of the way it captures New York City, his hometown.

The title may have been another matter. “Begin Again” was originally known as “Can a Song Save Your Life?”

Producer Judd Apatow seems to have made his peace with the rechristening.

“It’s an appropriate title for the movie and the movie is beautiful regardless of the title,” he said.

“Some people thought the other title might have been too dark,” Apatow added. “It’s hard to know. It had a lot of words in it, the old title. It would take up several rows of print.”

The red carpet unfolded inside a makeshift tent that grew increasingly greenhouse-like as temperatures rose and camera crews huddled to capture the film’s cast in their finery.

Asked if it was the hottest red carpet he’d ever been on, co-star James Corden quipped, “Yes, for all the wrong reasons.”

“My forehead at some point is going to explode,” he added.

After the screening, the afterparty continued at the Bowery Hotel.