Aaron Stewart is an American saxophonist and composer based in New York, and one of the more thoroughly recorded and least publicly documented reed players of the downtown and AACM-adjacent scene of the 1990s and early 2000s. No birth date or birthplace has been established in any published source. The earliest firm biographical fact on record comes from his alma mater: William Paterson University's jazz studies program lists him among its alumni as class of 1993, in a listing that summarises his career as "AACM projects, Vijay Iyer, Steve Coleman, Craig Taborn, Andrew Hill, Muhal Richard Abrams, Cecil Taylor, Anthony Braxton, David Murray Big Band, Collective Identity saxophone quartet."

His recording career begins almost immediately after that. On April 26 to 29, 1994, barely a year out of school, he was in East Side Sound in Manhattan playing tenor and soprano saxophone on Muhal Richard Abrams's septet date Song For All, released on Black Saint in 1997 alongside trombonist Craig Harris, trumpeter Eddie Allen, bassist Brad Jones, vibraphonist Bryan Carrott and drummer Reggie Nicholson. Abrams became the central figure of Stewart's early career: he performed with him frequently and studied composition with him, and he went on to appear in the AACM's own New York concert series as a sideman with Abrams, George Lewis, Reggie Nicholson and Ed Wilkerson. In the same years he was one of the players in Cecil Taylor's 35-musician ensemble during its weekly residency at the Knitting Factory.

The Knitting Factory was also where his long association with Anthony Braxton was documented. On November 24, 1995, Stewart played tenor in the large ensemble Braxton assembled for the Tri-Centric Festival there, a single continuous performance issued as Ensemble (New York) 1995 on Braxton House in 1997. He premiered Braxton's Composition 189, written for ten instrumentalists, during Braxton's three-day Ghost Trance festival, and he was one of the featured solo instrumentalists in Braxton's opera Composition 162, Shala Fears for the Poor, recorded October 25 and 26, 1996 at the John Jay Theater in New York and released in 1999 as Trillium R. That is the one documented occasion on which Stewart is credited on baritone rather than tenor saxophone; among the other named soloists on the same recording was clarinetist Perry Robinson. Between those dates he recorded Vincent Chancey's Next Mode for the Japanese label DIW, in a quartet with bassist Fred Hopkins and pianist D.D. Jackson.

Two long partnerships took shape in 1996 and 1997. On August 5, 1996, at OTR Studios in Belmont, California, Stewart played tenor and soprano in the octet Vijay Iyer assembled for Architextures, his second album, released on Asian Improv Records in 1998 with Rudresh Mahanthappa on alto and Liberty Ellman on guitar. The following spring he took a tenor chair in Steve Coleman's Council of Balance for Genesis & The Opening Of The Way, recorded at Systems Two in Brooklyn in April and June 1997 and issued as a double album on RCA Victor; Stewart plays the whole of the Genesis disc, in a reed section that also held Ravi Coltrane and Greg Osby, with George Lewis on trombone and Iyer on keyboards. He was by then also the tenor voice of Collective Identity, the New York saxophone quartet completed by Jorge Sylvester on alto, Sam Newsome on soprano and Alex Harding on baritone, whose only album The Mass was cut on September 9 and 10, 1998 at Tedesco Studio in New Jersey and released by Palmetto in 2000. Stewart contributed one of its six compositions.

Late in 1998 and again in January 1999 he was at Hillside Sound Studios in Englewood, New Jersey, for the sessions that produced Anat Fort's self-produced debut Peel, joining the Israeli pianist's trio with bassist Andreas Henze and drummer Heinrich Köbberling on the record's two quartet pieces, "The Dance" and "The Bridge". In 1999 he was also commissioned as a composer by the New York multidisciplinary performance group Tonk, whose album The Fences Show carries one of his pieces.

The first half of the 2000s was his busiest recorded stretch. He was the saxophone voice in guitarist Rich Woodson's Ellipsis on both of that group's albums, Control And Resistance (Cuneiform, 2000) and The Nail That Stands Up Gets Pounded Down (2005), and he played in Assif Tsahar's large Zoanthropic Orchestra when it was recorded live at the Knitting Factory on February 5, 2001. With Iyer and drummer Elliot Humberto Kavee he formed Fieldwork, a collective trio organised, in the band's own description, on the model of a rock group rather than a jazz combo, using written material as raw stock for extended collective development. Their debut Your Life Flashes was recorded in a single day, March 27, 2002, at Sorcerer Sound in New York and released that October as the fifth title in the Pi Recordings catalogue; Stewart wrote two of its ten pieces. He also joined Andrew Hill's Point of Departure Sextet, appearing in the sixteen-piece expansion of it billed as the Sextet Plus 10 on Hill's A Beautiful Day (Palmetto, 2002) with Nasheet Waits on drums, and he recorded trombonist Brett Sroka's Hearsay in Brooklyn on February 24, 2001 in a group that included pianist Jason Moran, trumpeter Avishai Cohen and drummer Eric Harland.

Two further strands close out the documented career. Marty Ehrlich brought him into the posthumous Julius Hemphill projects, first for One Atmosphere on John Zorn's Tzadik label in 2003, where Stewart is credited on tenor saxophone and flute, then for the reconstituted Hemphill Sextet recorded live at the Jazz em Agosto festival at Lisbon's Calouste Gulbenkian Foundation in 2003 and issued by Clean Feed as The Hard Blues: Live In Lisbon. And he was the horn on Craig Taborn's electro-acoustic Junk Magic (Thirsty Ear, 2004), alongside violist Mat Maneri and drummer David King, a credit that carries over to the companion remix record issued the same month. After 2005 the recorded trail goes quiet. Steve Lehman took the saxophone chair in Fieldwork, and no album under Stewart's own name has ever appeared.

Stewart's playing belongs to the generation of New York reed players who moved fluently between the AACM's compositional large-ensemble tradition and the harder, rhythm-driven end of the downtown scene, and his credits are a fair map of that range: Abrams and Braxton at one edge, Steve Coleman's M-Base circle and Fieldwork's interlocking metric structures at the other. He is a tenor specialist who doubled where a score asked for it, on soprano for Abrams and Iyer, on flute for the Hemphill book, and on baritone for the one Braxton opera in which he was named a solo instrumentalist. What recurs across the leaders who hired him is the demand for a player who could read dense written material and then improvise inside it rather than over it: Braxton's Ghost Trance systems, Coleman's Council of Balance, Hemphill's sextet writing and Rich Woodson's angular through-composed lines all ask for the same discipline. Pi Recordings, introducing Fieldwork in 2002, placed him among "three of the creative jazz world's admired young session men," which is roughly how the record shows him, a first-call ensemble musician for composers rather than a bandleader. He is also a composer in his own right, credited with pieces on Collective Identity's The Mass and two of the ten on Fieldwork's Your Life Flashes, and commissioned in 1999 by the performance group Tonk.