Grant Stewart was born June 4, 1971, in Toronto, exposed early to Charlie Parker, Wardell Gray, and Coleman Hawkins by his father, a high school English teacher and semiprofessional guitarist who transcribed their alto solos for his son to play. Stewart started on alto saxophone at ten, and by fourteen was advanced enough that Toronto bandleader Pete Schofield, his first teacher, invited him to play professionally in Schofield's big band. At seventeen he switched to tenor and began playing with two of the Toronto scene's most respected figures, Pat LaBarbera and Bob Mover — Stewart has singled out Mover as one of his greatest teachers — while absorbing Sonny Rollins, John Coltrane, Don Byas, and Lester Young as his core influences. By eighteen he was leading his own quartet in Toronto, anchored by a regular gig at the C'est What café and pub.

He moved to New York at nineteen in 1990, initially finding work alongside guitarist Peter Bernstein and saxophonist Jesse Davis, and began studying with Donald Byrd, Barry Harris, and Joe Lovano. Barry Harris's own career, and his side of this teacher-student relationship, is covered in full in his JazzProfiles.com profile. When Smalls Jazz Club opened in Greenwich Village in 1993, Stewart became one of the players who built its identity, a relationship that has continued for more than three decades. He was also, while still in his early twenties, a member of the last sextet led by veteran trombonist Al Grey. His performing résumé since has run through Clark Terry, Etta Jones, Jimmy Cobb, Harold Mabern, Louis Hayes, Curtis Fuller, Brad Mehldau, Bill Charlap, Lewis Nash, Peter Washington, Peter Bernstein, Russell Malone, Larry Goldings, Harry Connick Jr., Mickey Roker, Cecil Payne, Dick Hyman, Herb Geller, vocalese pioneer Jon Hendricks, and — a striking crossover credit — opera soprano Renée Fleming, on her 2014 holiday album Christmas in New York. He has toured North America, Europe, Japan, Brazil, and Taiwan, was among the first jazz musicians invited to perform at the Hermitage Museum in St. Petersburg, Russia, and has been featured in the Guggenheim Museum's jazz series leading a trio that included drummer Jimmy Cobb.

Stewart made his leader debut with Downtown Sounds, recorded December 27, 1992, in New York with trumpeter Joe Magnarelli, pianist Brad Mehldau, bassist Peter Washington, and drummer Kenny Washington; released in 1994 on the Dutch label Criss Cross Jazz (catalog Criss 1085), it was named one of the Toronto Star's top five jazz albums of that year. A prolific catalog followed across three overlapping label relationships: further Criss Cross Jazz dates through the mid-1990s and 2000s; a run of Japan-only releases for Videoarts Music and Birds Records recorded at Sear Sound in New York for the Japanese market (Tenor and Soul, Estate, Shadow of Your Smile, Recado Bossa Nova, Plays Jazz Ballads, St. Thomas: Grant Stewart Plays Sonny Rollins); and, from 2007, a core body of work for Sharp Nine Records — Young at Heart, In the Still of the Night, Plays the Music of Duke Ellington & Billy Strayhorn, and Around the Corner — that most directly showcased his working quartet sound. Pianist Tardo Hammer, bassist Peter Washington, and, from 2005 onward, his own younger brother Phil Stewart on drums became his most consistent collaborators across this stretch, giving his catalog the cohesion of a genuine working band rather than a rotating cast of studio dates.

In 2005 Stewart began co-leading Reeds and Deeds, a two-tenor quintet with fellow saxophonist Eric Alexander, built around the classic hard-bop cutting-contest format of dual tenors trading over a shared rhythm section (pianist David Hazeltine, with bassists Peter Washington or John Webber and drummers Kenny Washington or Joe Farnsworth rotating through). The project produced three albums for Criss Cross — Wailin' (2005), Cookin' (2006), and Tenor Time (2011) — not two, as some earlier reference summaries have stated. From 2008 through 2015, Stewart was voted a "Rising Star" tenor saxophonist for seven consecutive years in the DownBeat Critics Poll, and was profiled in the July/August 2009 issue of JazzTimes.

The 2010s and 2020s brought a shift toward Vancouver-based Cellar Live/Cellar Music, run by producer Cory Weeds, which has issued most of his recent work: the live Live at Smalls (2012, recorded at the club with Hammer, bassist David Wong, and Phil Stewart), the vinyl-only Trio (2015), Roll On (2017, recorded in Toronto), Rise and Shine (2020), The Lighting of the Lamps (2022), and his most recent leader date, Next Spring (2025, recorded at Van Gelder Studio in November 2024). The Lighting of the Lamps, billed to the "Grant Stewart Quartet With Bruce Harris," reunited him with the trumpeter he had featured alongside on Harris's own 2017 leader debut, Beginnings — whose full story is told in Bruce Harris's JazzProfiles.com profile — and again as sidemen together on bassist Clovis Nicolas's Freedom Suite Ensuite (2017). Also on Beginnings, Stewart shared horn duties with alto saxophonist Dmitry Baevsky in a rotating cast alongside Andy Farber and Jerry Weldon; the two tenor-and-alto players are labelmates-in-passing on that one date rather than co-leaders of any project of their own. Elsewhere in the 2010s, Stewart recorded a notable session with pianist Johnny O'Neal and trumpeter Roy Hargrove, In the Moment (2017, Smoke Sessions Records), cut live in the studio a little over a year before Hargrove's death in November 2018. He also recorded Namely You (2019, Blau Records) with Italian pianist Fabio Miano in Paris. In fall 2020 Stewart married jazz vocalist Lucy Yeghiazaryan, and has since appeared as a featured sideman on her albums Blue Heaven (2019), Some Other Spring (2023), and Hey Love! (2026).

Away from the tenor, Stewart has spent years studying classical composition privately with Dr. Kendall Briggs of the Juilliard School, writing works for piano, string quartet, and wind quintet. His first large-scale composition, an eight-movement unaccompanied Requiem, was recorded with the Festino Chamber Choir and soprano Alexandra Makarova at the historic Lutheran Church of St. Katherine in St. Petersburg — the same city, fittingly, where his career had already reached a landmark at the Hermitage Museum — and released in 2018. He also currently serves as Artistic Director of the Tribeca Jazz Institute at the Church Street School in New York.

Stewart's tone and time feel come directly from the hard-bop and bebop tenor lineage he named as formative early on — Sonny Rollins, John Coltrane, Don Byas, and Lester Young — filtered through the classic-swing grounding of teachers like Bob Mover, Pat LaBarbera, and, in New York, Barry Harris. The two-tenor cutting-contest format of Reeds and Deeds, alongside Eric Alexander, put that big, unforced sound in direct dialogue with a modern peer and became a defining strand of his catalog in the 2000s. Just as telling is how consistently he has worked with the same handful of musicians — pianist Tardo Hammer, bassist Peter Washington, and his brother Phil Stewart on drums — across nearly two decades of otherwise-scattered label relationships (Criss Cross, Sharp Nine, Videoarts, Birds Records, Cellar Live), giving his discography the coherence of a real working band rather than a series of one-off studio dates. His parallel life as a classically trained composer, capped by a full-length unaccompanied choral Requiem, points to a range well beyond the hard-bop mainstream he's best known for.