Avi Bortnick was born in Petah Tikva, Israel. His family moved to the United States while he was young, and he grew up in St. Louis, Missouri, immersed in late-1970s funk, soul, and rock. He studied guitar locally with Peter Mayer and classical piano with Linda Meyer during high school. In 1983 he relocated to California and worked through African and Caribbean bands, an early credit trail that includes appearances on Kotoja's Freedom Is What Everybody Needs (1991) and Sawalé (1992). As a graduate student at the University of Florida in Gainesville, he founded the band What It Is, which built a following on the Southeast touring circuit and released Soul Pop (Boomerang Records, 1997) without ever landing a major-label deal.

In January 2000, working as an acoustical consultant, Bortnick flew to New York to audition for guitarist John Scofield, expecting little from the trip. Scofield wasn't looking for another straight-ahead jazz guitarist; he wanted someone who could lock into an R&B groove the way a great drummer locks into a pocket, a skill Bortnick has described as "a trance-like locking into a groove." The tour he was hired for was booked for five months. It ran four and a half years.

Bortnick played on all three albums in Scofield's "Überjam" trilogy: Überjam (Verve, 2002), Up All Night (Verve, 2003), and Überjam Deux (Verve, 2013, on which he also served as co-producer), an arc spanning eleven years. Überjam was recorded live at Avatar Studios in New York in the summer of 2001; once drummer Ben Perowsky's sampling duties passed to him, Bortnick became the band's live sample and loop programmer alongside playing guitar. For the title track, he built the sound bed around a Tibetan monk's throat singing in B-flat, captured on the built-in microphone of his sampler during an earlier tour through Italy.

He released his own debut, Clean Slate, in 2003, and went on to record three albums with vocalist Jihae: Elvis Is Still Alive (2008), Fire Burning Rain (2010), and Illusion of You (2015), the last of which was later featured on the Netflix series Altered Carbon. He also recorded and toured with Ghost Train Orchestra (Book of Rhapsodies, 2013, and Book of Rhapsodies Vol. II, 2017), Betty Black, Rene Lopez, and others through the following years.

Throughout, Bortnick has maintained a parallel career in acoustics. He is an adjunct professor of architectural acoustics at the University of Pennsylvania's Weitzman School of Design and has worked for decades as a professional acoustical consultant on building and venue acoustics.

Bortnick's playing is rooted in the funk, soul, and R&B he grew up on in St. Louis rather than in bebop lineage, which is precisely what drew Scofield to him: a rhythm-guitar sensibility built on pocket and groove instead of chord-voicing vocabulary. His work with Scofield's band extended that sensibility into live sampling and electronic texture, treating the guitar and the sample rig as parallel, independently controlled instruments rather than one feeding the other. Beyond the Scofield association, his catalog draws on Caribbean and African rhythmic language (from his early years playing in African and Caribbean bands) and Brazilian idiom (via his production work with vocalist Lica Cecato), giving his broader body of work a wider geographic range than the funk-jazz fusion he's best known for.