Alex Weitz grew up in Tucson, Arizona, and came up through the Tucson Jazz Institute, playing in its Ellington Band, the program's award-winning big band. He left Arizona for Florida and took both his undergraduate and graduate degrees at the University of Miami Frost School of Music, studying jazz saxophone performance and studio jazz writing. While at Frost he played in the Henry Mancini Institute Jazz Septet under the direction of trumpeter Terence Blanchard, and in 2013 DownBeat gave him its Student Music Award for outstanding undergraduate performance in the jazz soloist category.

His debut record, Chroma, arrived in March 2013, cut in Miami the previous October with pianist Nick Hetko, Jason Matthews on Rhodes, bassist Geoff Saunders and drummer Michael Piolet. Piolet has been with him ever since. By the time of the follow-up, Luma (March 2017), the band had settled into the quartet Weitz still leads: pianist Tal Cohen, bassist Ben Tiberio and Piolet, four players who first started working together in Miami around 2013. Luma was self-released on his own imprint with the catalog number AW0001. One of his compositions, "Song for Peace," was licensed as the theme music for a Swedish documentary.

Weitz moved to New York, the third city in which he has worked professionally, and in 2019 took second place at the Michael Brecker International Saxophone Competition in Eilat, Israel, an event held in conjunction with the Red Sea Jazz Festival and named for Michael Brecker. The same year ASCAP gave him a Herb Alpert Young Jazz Composer Award for "Rude Awakening," and awarded him a second one in 2021. He has also built a parallel career behind a camera: since September 2020 he has produced and shot the video for "Live at Emmet's Place," pianist Emmet Cohen's Harlem living-room livestream, and he is credited as session photographer or videographer on a string of Outside In Music releases by Javier Nero and the Dan Pugach Big Band rather than as a player on them.

The pandemic shutdown and the death of his father supplied the circumstances for his third album. A 2021 Pathways to Jazz grant from the Boulder County Arts Alliance helped fund it, and Rule of Thirds was premiered at the Tucson Jazz Festival in January 2023 before Outside In Music issued it worldwide on April 28, 2023. Its title works several ways at once: it is his third record, it names the three musical strands he draws on (straight-ahead jazz, classical music and rock-influenced odd-meter writing), it marks New York as his third professional city, and it completes a photographic naming sequence begun by Chroma (the color content of an image) and Luma (its brightness). Eight of the nine tracks are Weitz originals; the ninth is his arrangement of Cole Porter's "Love for Sale." "The Hive" is named for a vegan restaurant in Miami and takes its compositional twists from Joe Henderson; "Convent Court" is named for a Harlem street and was the first thing he wrote after arriving in New York; and the closing "Sonata for Fred," a saxophone-and-piano duet, is an elegy for his father and his father's love of classical music. Guests join the quartet on seven of the nine tracks: Emmet Cohen plays piano on 1, 6 and 9, Ari Hoenig drums on 1 and 8, trumpeter Marcus Printup appears on 6, and guitarist Yotam Silberstein plays on 2 and 5.

The quartet took the same book on the road and recorded Live at the Black Cat on August 19 and 20, 2023 at the Black Cat in San Francisco, released March 1, 2024 on Weitz's own ABW Productions. In 2024 the Alex Weitz Group was one of four finalists for the DC Jazz Festival's DCJazzPrix, alongside the Dabin Ryu Band, the Hiruy Tirfe Quartet and the Micah Thomas Trio. He has played Dizzy's Club, Birdland, the Jazz Standard, the Kennedy Center Millennium Stage, the Jazz Showcase, and the Monterey, Telluride, Tucson, South Beach and Red Sea festivals, and has taught at the Miami Conservatory of Music, Young Musicians Unite and Jazz Empowers. A run of singles since late 2025, "Supernova" (November 2025), "Parallax" (January 2026, with guitarist Charles Altura added to the quartet), "Silver Lining" (March 2026) and "In a Sentimental Mood" (June 2026), points toward a fifth record.

Weitz plays tenor with a clean, unforced center and an unusually even command of the horn's range, and reviewers have consistently split the same way about it: the technique is not in doubt, the restraint sometimes is. Jeff Becker, writing in Jazz Sensibilities in August 2023, praised the record's "authenticity" while arguing that on "Rude Awakening" and "Odyssey" the soloing "wanders," short on motif development and space; Brice Boorman at Chalked Up Reviews made the same objection about "Rude Awakening" and then named "Odyssey" the album's high point for Weitz's "most arching and consistent solo." What is less contested is the writing. His compositions pull deliberately in three directions, hard-swinging blues-rooted material in the Joe Henderson line, odd-meter pieces closer to instrumental rock, and openly classical episodes such as "Nocturne in C Sharp Minor" and "Sonata for Fred," and he keeps them on one record without treating any of the three as a novelty. He plays RS Berkeley horns, a Virtuoso tenor and an SS524 soprano.