LOS ANGELES, Jan 13 — Ten minutes into a recent recording session with a Grammy-winning producer they had never previously met, Julia Michaels and Justin Tranter, the in-demand pop songwriters of the moment, had a bouncy new hook.

“She’s a new girl now,” Michaels, 22, sang with finger-snapping pop-soul syncopation for maximum catchiness. Tranter thumbed the words into his iPhone, fleshing out Michaels’ lines, which alluded to liquor and Instagram. The pair petted each other’s tattooed arms while volleying ideas, never separating by more than a few feet until Michaels entered the vocal booth. Tranter, 35, called out suggestions and encouragement.

Less than an hour later, they had a story of feminine renewal — taken from Michaels’ life but sung from the male viewpoint — and a simple, layered keyboard demo. There were 10 minutes to spare before dinner, enough for J-Roc, the producer known for his work with Timbaland (Justin Timberlake, Beyoncé), to cue up a futuristic R&B track.

Within three minutes, Michaels had delivered another melody wordlessly into her phone, citing Radiohead as inspiration. “Hot butter on breakfast toast,” J-Roc said, approvingly.

That fresh perspective, along with speed and precision, has been the modus operandi for Michaels, a professional songwriter since her early teens, and Tranter, a former glam-rock frontman, throughout their radio-dominating hot streak. Last year, the unlikely duo scored four Billboard hits together (and some apart), including Good for You by Selena Gomez and Sorry by Justin Bieber, both of which peaked in the Top 5 on the Hot 100 and topped the pop airplay chart.

The pair’s other successes included Love Myself, the self-care anthem by Oscar-nominated actress Hailee Steinfeld (“It’s very clearly about masturbation,” Michaels said), along with tracks for Demi Lovato and Fifth Harmony. After helping elevate newer stars beyond their tween die-hards, Michaels and Tranter were courted for sessions with established icons like Britney Spears, Gwen Stefani, Courtney Love and John Legend.

“They became my go-to writers so quickly because their batting average was so, so high,” said Aaron Bay-Schuck, the president of A&R at Interscope, whose job includes finding big artists their hits. “They just kept delivering.”

In this age of carefully engineered hit-making, with upward of a half a dozen writers contributing to each potential smash, earning a song placement on a top-tier album is highly competitive. In addition to known quantities pitching songs on spec, major labels often convene so-called writing camps for their biggest artists, featuring an array of musicians from different worlds all gunning for the same finite track list.

Increasingly, as genre lines and principles continue to blur, indie-leaning musicians are making their living in the studio, not onstage, guiding the sounds of pop radio with near-anonymity. Following in the footsteps of 4 Non Blondes’ Linda Perry and Semisonic’s Dan Wilson, artists cultivating careers as writers include Miike Snow’s Andrew Wyatt and the Cardigans’ Peter Svensson.

“It’s very valuable to have people from different backgrounds and perspectives in a room together,” Bay-Shuck said of Michaels and Tranter.

Besides churning out irresistible radio candy, the duo have developed a proven knack for giving a relatable voice to stars’ public psychodramas. After delivering for both Bieber and Gomez — famous exes — at the moment of their professional maturations, the songwriters contributed to Stefani’s post-divorce comeback single, Used to Love You, a midtempo ballad from a 25-year pop veteran.

“I think when you know the story, it’s much easier to write,” Michaels said of her job as a pop-star counsellor and translator. “I’m just good at listening, taking exactly what they feel and putting it on paper. It’s a very therapeutic thing.”

Tranter often serves that same role for his songwriting partner.

“Julia writes the songs as if she’s the artist,” he said, estimating that Michaels leads 75 per cent of their studio time. “I’m the extra piece to the puzzle.” (Without Michaels, his credits include Fall Out Boy’s Centuries and new music for Joe Jonas’ DNCE.)

Because of Michaels’ age, demographic and recent successes, questions about the next step for her are inevitable. Songwriters like Sia, Ester Dean, Jessie J and Bruno Mars have attempted the leap from studio to stardom with varying degrees of success.

“There will be no shortage of labels that are interested in Julia as an artist,” said Bay-Shuck of Interscope. “Ultimately, she has to ask herself what she wants.”

For the moment, it’s not more spotlight.

“Now more than ever, because of social media, songwriters are getting way more attention,” Michaels said, adding that she often suffers from panic attacks and was only recently recognised in public for the first time.

“I write songs for myself, but I never keep them,” she said. “I’m like, ‘OK, that was my therapy — it’s out of my body now. I’m going to give it to somebody else, so it can be their therapy, too.’” — The New York Times