Don Baldwin was born Donald James Baldini in Racine, Wisconsin, on December 5, 1940. He started on violin in elementary school and won a scholarship to the Jacobs School of Music at Indiana University, where the required string methods classes put a cello and then a double bass in his hands. His published obituaries record that on the bass he "found his home." His first professional job was with the Indianapolis Symphony, and his earliest documented recording session belongs to that Indiana period: the original 1967 pressing of Jamey Aebersold's play-along LP A New Approach to Jazz Improvisation, cut with pianist David Lahm and drummer Stan Gage and engineered by Indiana University percussionist Jack Gilfoy, credits Baldwin on bass.

He left Indianapolis for Las Vegas to take the bass chair in Harry James's orchestra. That band recorded The Golden Trumpet of Harry James at Tutti Camarata's Sunset Sound in Hollywood in the spring of 1968, released on London's Phase 4 series with liner notes by Nat Hentoff, and Baldwin plays bass on it alongside Sonny Payne on drums and Jack Perciful on piano. He stayed in Las Vegas for roughly a dozen years, moving from the James band into the house band at Caesars Palace, before relocating to Los Angeles and going to work as a studio player.

The Los Angeles move put him in the Toshiko Akiyoshi / Lew Tabackin Big Band at the exact point where the band moved from promising to famous. Baldwin took over the bass chair from Gene Cherico after Long Yellow Road, first appearing on Tales of a Courtesan (Oirantan), recorded December 1 to 3, 1975 at the Sunset Highland studio in Los Angeles. He then anchored the band's first live album, the double LP Road Time, taped January 30 and February 7 and 8, 1976 at Nakano Sun Plaza in Tokyo and at Sankei Hall and Kosei Nenkin Kaikan in Osaka, which drew a 1977 Grammy nomination for Best Jazz Performance by a Big Band. Insights followed at RCA Studio A in Hollywood on June 22 to 24, 1976, the record that won Down Beat's 1978 critics' poll as Jazz Album of the Year, took Swing Journal's Gold Disk in Japan, and earned another Grammy nomination. March of the Tadpoles was cut in the same room on January 10 and 11, 1977, and the band's June 29, 1977 set at the Newport Jazz Festival in New York yielded two separate albums, Live at Newport '77 and Live at Newport II. Between the big band dates he also played the small-group session Day Dream, recorded with Lew Tabackin and Toshiko Akiyoshi in Tokyo on February 12 and 14, 1976 and in Hollywood on March 8, 1976.

His one co-billed record came out of the same circle. Stepping Out, issued in 1977 on the Japanese label Discomate as the third entry in a series Akiyoshi produced for the label, is a septet date drawn straight from the big band's ranks: Steve Huffsteter on trumpet, Bill Perkins on baritone, Dick Spencer on alto and soprano, Tom Peterson on tenor and soprano, Bill Reichenbach on trombone, Peter Donald on drums, and Baldwin on bass, with all seven names printed across the sleeve and no single leader. The program mixes originals by Peterson, Reichenbach and Huffsteter with two Billy Strayhorn pieces, "A Flower Is a Lovesome Thing" and "Passion Flower."

Baldwin left the Akiyoshi band after 1977 and spent the following decade inside the Los Angeles studio economy, where his jazz credits mostly stop appearing on record sleeves and start appearing on screen. By his own account and his obituaries he played film and television scores, worked as the bassist for the Shubert Theatre, and held a chair in the "Tonight Show" band, a stretch one obituary puts at thirteen years. He toured with Johnny Mathis, Peggy Lee and Tony Bennett, and from roughly 1984 to 1987 he traveled the world as Frank Sinatra's bassist. That last job is the one that reached commercial release long after the fact: Concord's 2009 album Live at the Meadowlands, drawn from a Sinatra concert of the period, credits him on bass under the name Don Baldini.

He moved to New England around 1990 and stayed for the rest of his life, settling in Westminster, Vermont. For more than twenty-five years he was artist-in-residence at Keene State College in New Hampshire, where he conducted the orchestra and directed the jazz ensemble and taught theory, string methods, jazz history and sight-singing; he was also lecturer in double bass at Dartmouth College. He played with the Vermont Symphony Orchestra, Opera North, the Keene Chamber Orchestra and the Peterborough Players, and recorded with Erich Kunzel and the Cincinnati Pops. He retired from both colleges in December 2016 and made furniture, building pencil post beds and Windsor chairs. Baldwin passed away of cancer at home on March 4, 2024, at 83.

Baldwin was a conservatory-trained bassist who spent his career making other people's ensembles work, and the Akiyoshi band is where that shows most clearly. Akiyoshi's charts for Insights and March of the Tadpoles stack Japanese percussion, Noh chant, and unusual reed voicings on top of a conventional big band rhythm section, which leaves the bass with an unglamorous but load-bearing job: hold a fixed pulse under writing that keeps changing meter and texture, without pulling attention. Reviewers of those records praised the compositions, the reed section and Tabackin's solos, and almost never singled out the bass chair, which is a fair description of what the chair was for. His formal training is audible in the tone rather than the phrasing, and it explains a career that moved between the Indianapolis Symphony, the Harry James band, Caesars Palace, a Grammy-nominated jazz orchestra, the "Tonight Show" band, Frank Sinatra's touring group and, finally, the Vermont Symphony, without ever settling into a single idiom.