Bert Seager has been a fixture of the Boston jazz scene since 1981. He double-majored in economics and music at Haverford College, then earned a master's degree from the New England Conservatory in 1984, where he studied with Fred Hersch, Tom McKinley, and Jaki Byard, and privately with Charlie Banacos. He has taught at NEC's Contemporary Improvisation department ever since, an unbroken four-decade thread between his own playing and the generation of Boston-trained improvisers who came up under him.

His recording career opens with the Bert Seager Jazz Quintet, formed with trumpeter Tim Hagans and drummer Joe Hunt. Time to Burn (recorded April 1986, released 1987 on Antilles) paired Seager and Hagans with alto saxophonist Jimmy Mosher and bassist Dan Greenspan; Seager's own site cites it as a New York Times "Jazz Album of the Week," a claim repeated across his own bio pages that could not be independently traced to an archived Times review in this pass. The quintet's second Antilles date, Because They Can (recorded July 1987, released 1988), swapped in tenor saxophonist George Garzone for Mosher — the recorded root of a collaboration between Seager and Garzone that both musicians' JazzProfiles.com profiles now cite. A third quintet date, Live at the Yardbird Suite (1990, L+R Records), recorded with Billy Drewes on tenor and Ian Froman on drums, closed out the group's run on record.

Through the 1990s and 2000s Seager shifted the working unit down to a trio, and the personnel around him reads as a map of Boston's jazz-education pipeline: bassist Dan Greenspan and drummer Joe Hunt anchored his earliest sessions; later trios brought in bassist John Lockwood and drummer Kazumi Ikenaga, under the group name KJB, for Openings (2004), A Closer Look (Invisible Music Records, c. 2006–07), and Near and Far (2009); and a Peru-to-Boston pairing of bassist Jorge Roeder with drummers Jorge Pérez-Albela and, later, Richie Barshay carried Lima Beans (2009) and Lettuce Play (2011). Seager's own bio names Joe Lovano, Bob Moses, and John Lockwood among his regular collaborators alongside Garzone and Hagans, and credits stage work with George Mraz, Miroslav Vitous, Mick Goodrick, and Tom Harrell. One outlier in the catalog, 1985's Arise by the group Mili — led by vocalist Mili Bermejo — was produced by pianist Fred Hersch, Seager's own NEC teacher, with Seager on piano and electric piano alongside percussionist Cyro Baptista and bassist Oscar Stagnaro.

Seager's more recent work has moved toward quartet writing built around a single working group. Tetraptych (2017, Red Piano Records), with tenor saxophonist Hery Paz, bassist Max Ridley, and drummer Dor Herskovits, became the subject of a feature by his alma mater, Haverford College. The same quartet, expanded to include vocalist Lili Shires, became Heart of Hearing, which has released a new album roughly every year since 2023: Heart of Hearing (2023), Generosity (2024, with saxophonist Rick DiMuzio and bassist Max Ridley), and Kindness (2025, with bassist Andrew Schiller). Seager has also continued reworking earlier compositions on newer recordings — Dinner Music (2020) revisits material from Open Book, Pioneer, Lettuce Play, and Lima Beans — and his own site lists a further recent, as-yet-undetailed title, Life as Meditation.

Beyond performing, Seager has toured extensively both nationally and internationally, including twelve tours of Japan and stops in China, Hungary, Bulgaria, Ecuador, Peru, Canada, Israel, and Jordan. He is a three-time recipient of an extended composition residency at the MacDowell artists' colony in Peterborough, New Hampshire (2007, 2008, and 2012), has received a National Endowment for the Arts grant for jazz, and is an official Steinway artist.

Seager works in a post-modern, modal vein shaped directly by his New England Conservatory teachers — Fred Hersch, Jaki Byard, and Charlie Banacos among them — and by decades of working trio and quartet writing rather than a standards-repertoire approach. Critics have consistently pointed to the same balance in his playing: Cadence Magazine has described his music as carrying "effervescent optimism," the Boston Globe credited him with the "kind of exuberance [that] makes the jazz world go round," and Steve Elman of The Arts Fuse called him "one of our valuable local treasures." AllMusic's Michael G. Nastos located the same quality inside the writing itself, praising the "innate beauty and serene confidence" in Seager's compositions — a fair summary of a catalog that moves between hard-bop quintet dates, spare piano trios, and, in his more recent Heart of Hearing quartet, vocal-forward songwriting without losing its improvisational center.