Courtney Barnett plucked the title for her debut album, Sometimes I Sit and Think, and Sometimes I Just Sit, from a quote by Winnie-the-Pooh author A.A. Milne that graced a poster in her grandmother’s bathroom.

Barnett doesn’t just sit very often though, as the rising Australian indie-rocker busily traverses time zones. But she does a lot of thinking, observing seemingly mundane objects and interactions with a keen eye, processing the dread and humor of everyday life through a very active mind.

“It’s constantly churning, which can be a fucking nightmare,” Barnett says.

Luckily, that head gets emptied on a regular basis. The singer/guitarist jots her experiences and anxieties in a journal, eventually transforming those impressions into a sprawling flow of half-spoken lyrics, at turns clever and poignant—and playfully parsed in her accented drawl.

“I just kept trying different processes,” Barnett, 27, says from her home in Melbourne. “I would kinda read stuff over bits of music I’d written and let it piece itself together.”

America discovered her gift through last year’s sleeper hit “Avant Gardener,” a woozy account of an allergy attack from The Double EP: A Sea of Split Peas. Adrift in the song’s melodic swells, she drops ebb-and-flow deadpan couplets like “I’m breathing but I’m wheezing, feel like I’m emphysema-in’ ” and “The paramedic thinks I’m clever cos I play guitar, I think she’s clever cos she stops people dying.”

She spins her lyrics from real life, despite some sly exaggerations like that song’s “adrenaline straight to the heart” line, where Barnett name-drops Uma Thurman in a nod to a scene from the movie Pulp Fiction. “I got a shot in my thigh,” Barnett admits. “Everything else is pretty much a 95 percent true happening and true detail.”

Barnett has cultivated a broader, more buoyant collection on Sometimes I Sit and Think, and Sometimes I Just Sit, released in March. Suburban house hunting, roadkill and lovesick sleeplessness provide lyrical fodder, while the music expands to the ’60s-tinged pop hop “Debbie Downer,” the dreamy surf-blues “Small Poppies” and the self-loathing, Nirvana-esque blast “Pedestrian at Best,” in which Barnett barks, “Put me on a pedestal, and I’ll only disappoint you.”

The album peaks in the brooding, psychedelic “Kim’s Caravan,” which Barnett says she wrote after a trip to a friend’s coastal retreat near Melbourne, stressed about rounding out the album with more material. “I basically hit a real wall and just went into a bit of a dark place and got writer’s block for the weekend and got nothing done,” she says, “at a loss about me and the world around me.” Walking the beach, she saw a dead seal, which surfaces in the lyrics along with the Great Barrier Reef. “It’s been raped beyond belief, the dredgers treat it like a whore,” Barnett sings, shortly before the song hits a Crazy Horse-like guitar crescendo.

“The anger and frustration in some of the songs is the helplessness and feeling that you’re incapable of helping or making any sort of change,” Barnett says, “watching people be idiots around you.”

She hails from an arts-minded family near Sydney. Her mother was a ballet dancer and her father a graphic designer who “mostly listened to jazz and classical,” so

Barnett was introduced to rock through an older brother. She was into Nirvana by age 10, picking out “Come as You Are” on guitar, and moved on to Guns N’ Roses, Television, Talking Heads, and the Presidents of the United States of America, a band ripe with quirky lyrics. She wrote a bit of poetry and then studied art at the University of Tasmania (her drawings grace her album covers) before moving to Melbourne, where she played in garage-grunge and psych-country bands.

Barnett also bartended at a social club, a job she finally had to quit as her global demand grew, though she was back to playing with friends on a recent weekend home. “I’m still doing the same things, just sometimes on a bigger scale,” says the singer/guitarist, whose trio rocks the Sinclair on May 18 and the Newport Folk Festival on July 25. “You’re just playing music. It’s cool, wherever it is.”

Courtney Barnett plays the Sinclair on May 18.