Shirli McAllen pursued a singer-songwriter career in Los Angeles for years. She wanted to move people, make them weep. But that was before McAllen co-composed “Game Called Life,” a song destined to be the theme song for the Laura Linney-starring Showtime series, The Big C.

“Game Called Life” came to life after McAllen’s ukulele- and bass-playing friend, Austin Nicholsen, brought the smaller of those instruments over to her place one night.

“We didn’t set out to even write a song,” McAllen, lead vocalist for the L.A.-based, touring Leftover Cuties, said last week from upstate New York.

“Austin just came into my house and started playing these chords,” she continued. “I had written some lyrics that night at the bar where I was working, so I started singing over whatever he was playing. We wrote that song and really didn’t think much about it. We were just having fun.”

McAllen and Nicholsen made a quick recording of “Game Called Life” the next day, so they could revisit the song down the line, if they so desired.

McAllen stumbled upon the song in her computer a few years later.

“There was something special about it,” she said. “I played it for some friends. They all really, really liked it. They encouraged us to write more songs like that.”

Inspired, McAllen phoned Nicholsen.

“I said, ‘Austin, come back with your ukulele.’ And we started writing songs very quickly. It’s easier in a way, to do that in the beginning, because you have no songs. It was an incredible time. I never thought it would be so fun and so easy.”

The new songs McAllen wrote with Nicholsen were unlike the melancholic singer-songwriter material she’d been writing. McAllen soon found that making people smile was vastly more satisfying than making them weep.

“At our shows, people smile from ear to ear,” she said. “It’s a really great feeling. People shed tears at our shows, too, because not all of the songs are about happy things. But the majority of the time, people really feel happy when they hear us.”

There was more to come, too, for “Game Called Life,” the song that set McAllen, Nicholsen and Leftover Cuties on their new musical course.

The band made “Game Called Life” the title track for its 2009 EP. About a year later, the music supervisor for The Big C discovered the song.

“She happened to have our EP because we sent it to everybody we knew, or everybody who our friends knew,” McAllen said. “Our song was chosen out of a hundred choices that she gave the producers of The Big C.

“They weed it down to 10 to 20, to the last 10, to the last three. And then you’re left with the one that everybody loves and thinks is the best fit. So that’s how these things pretty much happen.”

Since “Game Called Life,” the song composed so spontaneously, then forgotten about and then rediscovered, became The Big C theme, people throughout the world have contacted Leftover Cuties.

“A lot of viewers of the show told us they’ve made it their own personal theme song,” McAllen said. “That was extremely moving, to have the song do more than you even intended for it to do. It’s the beauty of interpretation.”

The song’s placement in the series also brought Leftover Cuties attention in McAllen’s native Israel.

“My parents are very proud of it,” she said.

Leftover Cuties, on a North American tour following last month’s release of their second album, The Spark & The Fire, is playing its first New Orleans area show Monday at Ruby’s Roadhouse in Mandeville.

The band’s eclectic range, from classic rhythm-and-blues to traditional jazz to ’60s pop, suggests the wide range of styles performed by the tradition-informed young bands of New Orleans.

“We never limit ourselves to a certain thing,” McAllen explained. “More than anything on this new album, we took each song and crafted everything, what we thought was best for that particular song, around it.”