Pop has its Michael and Janet. But in the realm of sensitive hipster rock, Rufus and Martha are the sibling singer-songwriters to watch. Rufus, of course, is Rufus Wainwright, son of quirky folk legend Loudon Wainwright III and Kate McGarrigle of the hippie sister act Kate and Anna McGarrigle. And Martha is his 25-year-old sister, a powerful musician in her own right who is just now gaining recognition for her smoky-voiced ballads and swooning melodies. The youngest in the line of Wainwright-McGarrigles, which includes a bevy of cousins, Martha will appear at the Brooklyn Academy of Music’s BAM Cafe tomorrow night performing music from her recently released self-title debut CD. But that doesn’t mean she’s above singing backup for her big brother.

On Tuesday, from a quiet corner on the “Tonight Show” set, she phones during a break in rehearsals for Rufus’s appearance later that day. On camera, she’ll wear black and harmonize behind him and just a bit to the right, as is the norm. But unlike most backup girls, Martha has her own spotlight, and she draws the camera like a star. Being part of a famously musical family has its benefits — and its drawbacks.

Martha and Rufus have been singing together ever since the Wainwright-McGarrigle clan — undoubtedly the most glamorously bohemian family on their block in Montreal — used to hit the road ensemble during summer breaks from school. “We would sort of loosely plan a vacation around a tour,” says Martha, who now lives in Brooklyn. The kids sang backup while their parents took center stage. “It wasn’t like the Partridge Family,” she says. “Our parents weren’t taskmasters. I always wanted to go on stage and I wish that I could be on longer every time.”

Some families might pass along granny’s jewels, but for this clan, crooning together is a true family tradition. Martha toured with her father as his opening act a few years back, and while she found his professional pointers “very annoying,” traveling together provided invaluable time together. “We really got to know each other better,” she says. “Just having dinner with your dad every night is something I never really had the chance to do.” Still, as cool and indie as hers may be, parents will be, well, parents. “Touring with my dad was a constant struggle,” Martha admits. “It’s all about proving yourself to your parents in order to move on.”

But that urge to forge ahead didn’t stop Martha from jumping on the bus once Rufus kicked off his tour. “We’re very close,” she says. “Touring together is about being young and having a great time and bringing really great music to people who don’t get to hear really great music. It’s not guitar rock, it’s serious, beautiful stuff.”

The family legacy also has provided a strange fan base for the singer. Younger fans, whom she calls “music lover hipsters,” have no idea who her parents are and simply find themselves drawn to Martha’s dreamy guitar, raw voice and witty lyrics. “He’s Laurel. /He’s Hardy./ He’s the life of the party/ and he’s got great taste in furniture,” she croons during “Laurel & Hardy,” a song Martha wrote about her brother. But followers from the baby-boom generation first saw Martha on tour with her mother, or opening for her father.

These days, however, Wainwright has her heart set on singing solo. “I’ve been very distracted by my family. I’ve done a lot of backup singing for them and given a lot to that,” she says. “I’m at the beginning of something that I hope will flourish.” To follow her debut album, Wainwright hopes to make a record that people will be listening to 20 years down the road.

That wasn’t always her dream. As a young teenager, Martha even found herself bucking the family tradition. “I liked to sing pop songs,” she says. “But I wasn’t picking up the banjo or learning to play the fiddle or anything. I was afraid of totally getting involved in music.” In order to define herself, Martha gave up singing in favor of acting for a few years. But she couldn’t deny the inevitable — or her love of music — for long. By the time she was 18, she had taught herself to play guitar, given up listening to pop in favor of Leonard Cohen, Nick Cave and Patti Smith and took to performing solo on Montreal’s cafe circuit. “It was far more fun to play out than to do my homework,” she says.

Her solo act also offered a chance to step out of the shadows and, through the moody melodies of her folk fusion sound, express her rawest emotions. “I had always learned to sing harmony with my brother or my cousins, and this was an opportunity to not meld with anybody but to sing by myself,” she says. “Now, when I’m singing and playing, it’s like I’m turning myself inside out.”

As much as she’d like to distance herself, exposing the personal also seems to be a genetic predilection. Just as Rufus first came to be known in folk circles via Loudon’s song “Rufus Is a Tit Man,” written when the now-fabulous performer was still a suckling infant, the first song Martha wrote, “Lexi,” was about her newborn half-sister.

Loudon’s career in the underground has always been pushed along by his uncanny ability to divulge both the bright spots and dark corners of daily life through his lyrics. He commemorated Martha’s fifth birthday in one song, divulged the gruesome details surrounding his 1979 break-up with Kate over the course of many, and in “Hitting You,” offered a guilt-filled reverie about the time he struck his daughter, a song she has sung with him on stage.

The children have continued mining familial relations for material. “Rufus wrote one song about me, one about my dad and one about my mother,” Martha says. “He was very democratic about it.” For her part, although Martha also started out writing about her family, now she’s moving along. “The first songs I wrote were a lot about my brother and a lot about my dad because I was trying to exorcise that in some way,” she says. “But eventually, you know, you fall in love with some guy and you break up and you’ve got many songs worth of material. Then you wait for the next one to come along and the next heartbreak.” Spoken like a true Wainwright.

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