Jessy J was born Jessica Arellano on December 20, 1982, in Portland, Oregon, and grew up in Hemet, California. Her father is from Mexico and her mother is from Texas. She started on piano at four, and at fifteen she won the piano state championship at the Béla Bartók festival. She also played saxophone in state honor bands, including a Grammy band, and her biography adds festival dates abroad, among them the Montreux Jazz Festival. A scholarship took her to the University of Southern California, where she earned a degree in jazz studies and was named her class's most outstanding jazz student. At USC she was chosen two years running for Disney's All American College Band, and in 2010 she was inducted into Disney's Magic Music Days Hall of Fame.

Before her own records she worked as a stage performer and hired player. She was in the casts of Mason Entertainment Group's shows Shockwave, Cyberjam and M.I.X., as saxophonist, singer, actress and dancer, on tours of the United States, the United Kingdom and Japan. Television appearances in 2006 with the pop singer Jessica Simpson (The View, Good Morning America and the NBC Rockefeller Center Christmas tree ceremony) were followed by a 2009 spot on Good Morning UK with Seal and a 2009 Royal Albert Hall concert special with Michael Bolton. Her biography also lists touring with The Temptations and studio work with Michael Bublé.

Her recording career began when the producer and guitarist Paul Brown heard her demo and gave her a place in his touring band. All About Jazz dates her first show with that band to Valentine's Day 2006 in Fresno, California. Her first major solo date was the Catalina Island JazzTrax Festival later that year, and in 2007, the festival's twentieth anniversary, she headlined all three weekends. A self-titled album appeared that year and, by All About Jazz's account, made little impression. Tequila Moon (Peak Records, distributed by Concord, March 4, 2008) was produced by Brown, and its title track spent seven weeks at No. 1 on Billboard's smooth jazz airplay chart between late May and early July 2008. Radio & Records named her its Debut Artist of the Year, and she was on the cover of Jazziz in May 2008. True Love (August 4, 2009), again produced by Brown, brought a second airplay No. 1 for two weeks in October 2009 with "Tropical Rain," co-written with the keyboardist Gregg Karukas.

She toured widely as the albums came out. Her biography lists dates with Jeff Lorber, Jeff Golub, Euge Groove, Paul Brown and Gerald Albright, including the Guitars & Saxes tour of 2008 and 2009, and in 2010 she toured with Norman Brown and the singer Brenda Russell on the Summer Storm Jazz tour. Hot Sauce (Heads Up, a Concord imprint, September 6, 2011) added Joe Sample, Harvey Mason and the guitarist Ray Parker Jr. as guests, and it is listed as debuting at No. 1 on Billboard's jazz albums chart. Its title track reached No. 4 on the airplay chart that fall. All About Jazz's Jeff Winbush heard a reliance on formula in it, and he was warmer about its follow-up. Second Chances (Shanachie, September 10, 2013), which she produced with co-producers including Lorber, bassist Jimmy Haslip and the singer and trumpeter Johnny Britt, debuted at No. 2 on the same chart. The title track, with Norman Brown on guitar, reached No. 19 on the airplay chart in 2014. My One and Only One (Shanachie, May 26, 2015) reunited her with Brown and Karukas and included covers of The Cure's "Lovesong," Toni Braxton's "You're Makin' Me High" and Shuggie Otis's "Strawberry Letter 23."

From 2016 she has released her records on her own label, Changi Records. California Christmas (October 28, 2016) was the first of two holiday albums, and Live at Yoshi's: 10 Year Anniversary Special (April 27, 2018) marked a decade since Tequila Moon; "All I Want" from that live set reached No. 3 on the airplay chart in July 2018. Blue (April 15, 2022), written and recorded during the pandemic lockdowns, turned to the soul and blues of the 1960s and 1970s, with "Dance Beat" reaching No. 5 in November 2022, and her biography says the JazzTrax platform named it album of the year for 2022. California Christmas, Vol. 2 followed on October 28, 2022. In 2024 she released two children's recordings, an instrumental lullaby EP on May 10 and the sing-along album Now, Let's Play on July 26. Terranova (April 4, 2025) reunited her with Paul Brown as producer, and her biography calls it their fifth album together. It features the bassist Brian Bromberg. She was also booked at Yoshi's in Oakland on August 11, 2024.

Jessy J is a smooth jazz saxophonist first, and her records say so plainly: radio-ready grooves, a low, soulful tenor sound, short melodic hooks and a producer's polish. Her Latin side is the thing that sets her apart within the format. Samba and bossa nova come through in her covers of "Mas Que Nada" and of Sérgio Mendes's "Magalenha," in the Brazilian-flavored "Morning of the Carnival" from Black Orpheus, and in her English-language vocal on Antonio Carlos Jobim's "No More Blues." Her biography also stresses her Mexican-American roots, and Terranova includes "Piel Canela," a mid-1960s favorite of her father's. She also draws on pop, R&B and soul, from Phoebe Snow's "Poetry Man" and Roberta Flack's "Feel Like Makin' Love" to Grover Washington Jr.'s "Mister Magic" and the funk and blues colors of Blue, and she sings, in a light, breathy voice, on a number of tracks herself. Beyond the tenor she plays alto, soprano and baritone saxophone and flute, and she began on piano, which she has also played in studio sessions with Paul Brown.

The jazz connection is real but specific. She earned a jazz studies degree at USC, covers Duke Ellington's "In a Sentimental Mood" on Hot Sauce, and has toured with the smooth jazz circuit's Jeff Lorber, Gerald Albright, Euge Groove and Peter White. Her records, though, are made for smooth jazz radio, and the improvising on them serves the song form rather than the other way around. Critics have noted this from both sides. Jeff Winbush of All About Jazz called Hot Sauce a product of formula and Second Chances her most fully realized album, and Jonathan Widran of Music Connection described Blue as some of her most passionate playing. Woodrow Wilkins of All About Jazz observed in 2008 that the demo that won over Paul Brown was straight-ahead jazz, yet the relationship put her squarely in the smooth jazz format.