Joel Forbes was born in New Haven, Connecticut, on August 5, 1956, into a house where the music was already playing. His father, also Joel Forbes (1928 to 2002), was a pianist on the New York City scene; his mother, Claire Forbes, née Sheil, was born in New York in 1927, and his sister Meg in 1954. The son gave the father full credit for the ear he ended up with: hearing the great songs sung and played around the house from before he was born, he said, put the music in his heart, and playing gigs with him was lucky. The family lived in Manhattan for two years and then in Westchester County until he was nineteen. He spent a year in Telluride, Colorado, and studied bass privately with Lou Stelluti for three years, from 1976 to 1979. After college he moved back to Manhattan for a decade, 1980 to 1990, then to Greenpoint, Brooklyn, and from 1991 settled in Goldens Bridge, in northern Westchester, where he lived for the rest of his life.

The paper trail of his playing starts in the early 1990s. His own reference-book entry names a 1992 record with the singer Nicole Pasternak and tenor saxophonist Ralph Lalama as his first, though no copy of it could be located for this profile. The earliest session that can be verified from the release itself is January 1994, at Acoustic Recording in Brooklyn, for the Australian guitarist Steve Brien's Token Entry: Forbes played bass, co-produced the record, and was back at the same studio for a second batch of tracks in September 1995. It came out in 1996 on the Sydney label La Brava, with Dale Barlow and Lalama on tenors and Dave Panichi on trombone, and it is the first sign of an Australian connection that ran through his career. In December 1995 he was at Edison Studios in New York for trombonist Dan Barrett's Moon Song with singer Rebecca Kilgore, and in 1997 he led the onstage quartet for the American Place Theatre production of Carson Kreitzer's The Slow Drag, the Billy Tipton play built as a jazz cabaret with a live band. Two further leader credits exist only as his own claims: an album called The Joel Forbes Songbook dated 1996, and an unissued Joel Forbes Quintet set from the Guggenheim Museum's World Beat series in 2001. Neither has surfaced in any catalogue.

Barrett and Kilgore turned into a long association. Forbes joined BED, the trio band name Kilgore, Barrett and the guitarist and singer Eddie Erickson used for a few years, on Bedlam (2004) and Watch Out! (2006) for the small Blue Swing label. Adding a permanent bassist changed what the group was, and not long afterward they renamed themselves the Rebecca Kilgore Quartet. That was the world Forbes worked in for most of the 2000s: Arbors Records in Florida, Nagel Heyer in Hamburg, the classic-jazz party and festival circuit, and tours through the United States, Europe, Japan and Australia. He turned up on Bryan Shaw's Night Owl, on Barrett's International Swing Party, on a Lino Patruno tribute to Bix Beiderbecke taped at the Ascona festival in Switzerland in 2003, and on Wayne Escoffery's Times Change, cut in New York on January 4, 2001 and mixed in Hamburg that July.

The relationship that defined the second half of his working life was with tenor saxophonist Harry Allen. Forbes was the bassist in the Harry Allen-Joe Cohn Quartet, a working band with a run of Arbors albums beginning with Hey, Look Me Over in 2004 and continuing through Perform Music From Guys And Dolls (2007), Stompin' The Blues (2008) and Plays Music From South Pacific (2009). He was also the bassist in Allen's other regular quartet, with Rossano Sportiello on piano and Chuck Riggs on drums, which recorded for Challenge in the Netherlands (Hits By Brits, 2007; New York State Of Mind, 2009; Rhythm On The River, 2011; 'Round Midnight, 2012, with Scott Hamilton added), for the Japanese Swingbros label, and behind Kilgore on a string of songbook projects. The same trio without Allen made two out-of-print Japanese albums applying jazz treatment to classical themes, Schubert in Jazz and Liszt in Jazz, both 2011, neither of which Discogs carries. Allen's Rolodex is essentially Forbes's discography: of the forty-three releases Discogs credits to him, more than half are Allen's.

The other half of his week was downtown. The SmallsLIVE archive holds more than two hundred nights with Forbes on the bandstand at Smalls and Mezzrow between 2007 and 2018, most of them with the Grant Stewart Quartet or one of Allen's groups, and the rest scattered across Ralph Lalama's Bop Juice, Joe Magnarelli's quartet, the Ehud Asherie Trio, Sportiello's groups, John Bunch's trio and the Ken Peplowski Quartet. He recorded twice with Asherie: Lockout, the pianist's leader debut, cut at System Two in Brooklyn on February 5, 2007 with Stewart and Ryan Kisor, and Modern Life in 2010, an Allen quartet date with Riggs on drums. With Stewart he made two albums for the Japanese Videoarts label, Tenor And Soul (Sear Sound, March 7, 2005) and Estate (Avatar, December 8, 2005). Ralph Lalama's Bopjuice: Live At Smalls (2012) put him on the club's own label.

From the summer of 2007 he had a third life at the Ear Inn. The EarRegulars, the Sunday-night band Jon-Erik Kellso and guitarist Matt Munisteri started at 326 Spring Street on June 17 of that year, used Forbes as its bassist through its early seasons, playing the 1920s to 1940s repertoire in a front-line-and-rhythm quartet with no piano. Michael Steinman, who filmed the room for years, kept returning to the same point about the rhythm section: Munisteri and Forbes worked as one instrument. The same period took him to the Sweet and Hot Music Festival in Los Angeles in September 2011 and the Cleveland Classic Jazz Party in September 2017.

The one record billed with his own name on the front is I Walk With Music: The Hoagy Carmichael Songbook, recorded in a single day, January 9, 2013, at Trading 8s in Paramus, New Jersey, and credited to Sportiello, Allen and Forbes as equals. His last documented session was Allen's The Candy Men, cut August 19 and 20, 2015 and released on Arbors in 2016. He was then diagnosed with multiple sclerosis. Allen ran a fundraiser for him, describing a man who had been building an extension onto the Goldens Bridge house entirely by himself, rigging pulley systems to raise the walls, and who could no longer finish it. Forbes retired from music altogether. He died on December 27, 2024, at 68. Kellso, hearing the news two days later, wrote that he had known Forbes was getting sicker and it still felt like a gut punch.

Forbes played gut strings on an Eastern European bass perhaps twenty or thirty years old, held together, by the mid-2000s, with tape rather than glue, and he did not use a pickup: on a Sydney jam in May 2005 he simply had a microphone into the PA. That setup is the whole argument. The New York bass luthier Arnold Schnitzer, who called him "a heck of a player," noted that Forbes was a trained luthier himself who had grown tired of repair work and now preferred tape to hide glue, and that he had recently dumped a carload of old bass parts at Schnitzer's shop to be rid of them. The Sydney luthier who started that conversation described what he heard as a player who stayed almost entirely below the neck joint, with great time, a solid instrument and a marvellous sound, and who could build a solo in half position rather than escaping upward into thumb position. What Forbes offered was weight and placement rather than display. Kellso called him one of the best bassists he had played with; the recurring judgment on the Ear Inn nights is not about his solos but about the way he and Matt Munisteri functioned as a single rhythm-and-solo unit. He worked almost entirely inside the swing and mainstream tradition, and the small handful of harder bebop settings he appears in, Lalama's Bop Juice, Grant Stewart's quartet, Asherie's Lockout, show the same approach unchanged.