Walter David Weiskopf was born on July 30, 1959, in Augusta, Georgia, and grew up outside Syracuse, New York. He took up the clarinet at ten and moved to the saxophone four years later. He entered the Eastman School of Music at the University of Rochester in 1977 and finished a bachelor's degree in music performance in three years rather than four, then moved to New York City in September 1980. Within a year he had the kind of job most conservatory graduates wait a decade for: in 1981, aged twenty-one, he joined the Buddy Rich Big Band. He kept studying after that. In 1988 he enrolled at Queens College of the City University of New York, spent two years working on clarinet with Leon Russianoff, and took a master's degree in clarinet performance, a credential almost no jazz tenor player of his generation holds.

The Rich gig led directly to the long one. In 1983 Weiskopf joined the Toshiko Akiyoshi Jazz Orchestra and stayed fourteen years, until 1997, recording seven albums with the band and touring internationally throughout. He sat in a reed section alongside Lew Tabackin and, on some dates, Frank Wess, doubling tenor, soprano, flute and clarinet as Akiyoshi's writing demanded. That band is where his big-band reputation was made, and it is audible on the orchestra's Carnegie Hall Concert (Columbia, 1992) and Desert Lady / Fantasy (Columbia, recorded December 1 to 3, 1993). He later occupied the same kind of chair in the Vanguard Jazz Orchestra, on Forever Lasting: Live in Tokyo (Planet Arts, 2011), and in John Fedchock's New York Big Band and NY Sextet.

His own recording career began in 1989 with Exact Science on the small New York label Iris, a quartet with his brother, the pianist Joel Weiskopf, plus Jay Anderson and Jeff Hirshfield, followed by Mindwalking with the same band in 1990. The decisive move came in December 1992, when the Dutch producer Gerry Teekens recorded him for Criss Cross Jazz. Simplicity, cut on December 23, 1992 with Andy Fusco on alto, Conrad Herwig on trombone, Joel Weiskopf, Peter Washington and Billy Drummond, opened a run of eleven Criss Cross leader albums stretching to 2010, almost all of them recorded in a single December day in Brooklyn or Manhattan in the label's characteristic fashion. The formats varied more than the label's reputation suggests: A World Away (recorded December 21, 1993) is an organ quartet with Larry Goldings, Peter Bernstein and Bill Stewart; Song for My Mother (December 20, 1995) and Siren (December 21, 1999) are nonets with a four-flute-and-reeds palette built for Weiskopf's own arrangements; and Man of Many Colors (December 12, 2001) is a pianist's-choice quartet with Brad Mehldau, John Patitucci and Clarence Penn.

Alongside all of that, Weiskopf built the career he is most widely recognized for outside the jazz audience. He joined Steely Dan in 2002 and played on Everything Must Go the following year, taking the tenor solo on the closing "Slang of Ages" and switching to alto on the opening "The Last Mall." From 2006 he worked in Donald Fagen's band, appearing on Morph the Cat and Sunken Condos (2012), and from 2010 in the Dukes of September, the Fagen, Michael McDonald and Boz Scaggs revue documented on Live at Lincoln Center (429 Records, 2014). He was still in the horn section for the pair of live albums the organization released on the same day in September 2021, Steely Dan's Northeast Corridor and Donald Fagen's The Nightfly Live. It is unusual for a working post-bop leader to hold a rock touring chair for two decades without either side of the résumé thinning out, and Weiskopf's did not.

From 2014 he moved his leader dates to Marc Free's Posi-Tone label, and the four albums he made there sharpened the group sound considerably. Overdrive (recorded October 29, 2013 at Acoustic Recording, Brooklyn) is a sextet with the vibraphonist Behn Gillece, the pianist Peter Zak, the guitarist Yotam Silberstein, the bassist David Wong and the drummer Donald Edwards. Open Road (2015) stripped back to a quartet with Zak, Mike Karn and Steve Fidyk. The Way You Say It, recorded September 29, 2015 and released April 8, 2016, replaced the piano with Brian Charette's organ and kept Gillece and Fidyk, producing the leanest and most groove-driven record in his catalog. Fountain of Youth (recorded September 27, 2016) reunited the Zak and Gillece front line. Since 2018 his main project has been the Walt Weiskopf European Quartet, a Danish band with the pianist Carl Winther, the drummer Anders Mogensen and, after a first album with Daniel Franck, the bassist Andreas Lang. That group has issued a steady run on Orenda and then on his own AMM imprint, including Worldwide (2019), Introspection (2020), Diamonds and Other Jewels (2022) and Harmless Addiction (2023), and it is the band he toured Europe with through the 2020s.

Teaching and writing have run in parallel throughout. Weiskopf was an adjunct professor at New Jersey City University from 1996 to 2000, a visiting associate professor at his own alma mater, the Eastman School of Music, from 2001 to 2009, and a part-time instructor at Temple University in Philadelphia from 2010 to 2012, before returning to New Jersey City University as Coordinator of Jazz Studies. His eight books for Jamey Aebersold, several co-written with Ramon Ricker, are standard equipment in university jazz programs: Coltrane: A Player's Guide to His Harmony (1991), The Augmented Scale in Jazz (1993), Intervallic Improvisation (1995), Around the Horn (2000), Beyond the Horn (2006), Giant Steps: A Player's Guide to Coltrane's Harmony (2010) and Understanding the Diminished Scale (2013) among them.

Weiskopf plays with a broad, centered tenor sound and an unusually even attack across the horn, and the thing that separates him from his contemporaries is what he does with intervals. Where most post-Coltrane tenor players build lines out of scale fragments, Weiskopf builds them out of wide leaps, a method he codified in Intervallic Improvisation and applied on record long before he wrote it down. His two acknowledged starting points are John Coltrane, whose harmony he has spent two books analyzing, and Sonny Rollins, and JazzTimes has described him as taking "the kinetic modulations of John Coltrane" together with Rollins's lyrical imagination while remaining his own player. Almost all of his leader albums are dominated by his own writing, and his arranging is the other half of the case for him: the two Criss Cross nonets, Song for My Mother and Siren, score flutes, alto flute and bass clarinet against a conventional bop rhythm section in a way that owes more to his fourteen years inside Toshiko Akiyoshi's orchestra than to any small-group model. JazzTimes named him one of the five most underrated players in jazz in 1997, and Song for My Mother took four stars in DownBeat.