Kenneth Joseph Peplowski was born May 23, 1959, in Garfield Heights, Ohio, a Cleveland suburb, to Norbert and Estelle Peplowski. His father was a police officer who also led an amateur Polish polka band, and Ken and his trumpet-playing older brother Ted played weddings and dances in it virtually every weekend through high school, making local radio and television appearances along the way. He later called the polka band his real music school: "That's where I learned to improvise, 'fake' songs, learn about chord changes, etc. It's exactly like learning to swim by being thrown into the water." He played his first professional engagement while still in elementary school, was experimenting with jazz in his school's stage bands by his early teens, and was teaching at a local music store and gigging around Cleveland while still in high school. After a year of college, he was heard at a Cleveland jazz festival, on the same bill as Duke Ellington and Teddy Wilson alumni, by trombonist Buddy Morrow, who led the touring Tommy Dorsey Orchestra. Morrow hired him on the spot, both for the lead alto chair and for a nightly clarinet feature with the rhythm section. Peplowski toured with the band for roughly two years, calling it "a great road-school," met the saxophonist Sonny Stitt on the road and studied with him, and by his own account moved to New York in 1980 on Morrow's advice not to "go back to Cleveland and be a big fish in a small pond."

In 1984 Benny Goodman came out of retirement to form a new band and hired Peplowski on tenor saxophone; he stayed until Goodman's death in June 1986, appearing on the clarinet legend's final studio recording, Let's Dance. Concord Records signed him under founder Carl Jefferson, and his debut as a leader, Double Exposure, was recorded in 1987 and released in 1988 with Ed Bickert, John Bunch, Terry Clarke and John Goldsby. Concord became his main label through the 1990s: by his own count he made close to twenty albums there, running from Sonny Side (1989) and Mr. Gentle and Mr. Cool (1990) through The Natural Touch (1992), which won Best Jazz Record of the Year from the German critics' award Preis der deutschen Schallplattenkritik, to The Other Portrait (1996), recorded in Sofia, Bulgaria with a symphony orchestra to showcase his classical side, and Grenadilla (1998). The same years produced a long sideman list for the label: four albums each with Mel Torme and the singer Susannah McCorkle, four with the guitarist Charlie Byrd, records with Hank Jones, George Shearing, Peggy Lee and Leon Redbone, and the soundtrack to Woody Allen's Sweet and Lowdown (1999).

The 2000s scattered his leader catalogue across labels and continents. He recorded for the German label Nagel Heyer (Lost in the Stars, 2001; Easy to Remember, 2004, which carries singer Bobby Short's final recording), for the Japanese audiophile label Venus (Memories of You, 2006; When You Wish Upon a Star, 2007; the Ken Peplowski Gypsy Jazz Band's Gypsy Lamento, 2008), and, from 2007 on, for Arbors Records in the United States, beginning with Dialogues and Dearest Duke. That year he was also named jazz advisor of the Oregon Festival of American Music and music director of its Jazz Party at The Shedd in Eugene, the first of several festival-director posts he held alongside performing, and he began a long run of duo and small-group albums in Britain with the saxophonist Alan Barnes on the Woodville label. In the 2010s he added Capri Records to the list of homes (Noir Blue, 2010; In Search Of..., 2011; Enrapture, 2016) while continuing to tour internationally; a January 2017 performance at the Festival Internacional de Jazz de Punta del Este in Uruguay put him in a working quartet with the pianist Ehud Asherie, bassist David Wong and drummer Matt Wilson, with Paquito D'Rivera sitting in as a special guest.

That quartet's pianist became the anchor of Peplowski's next studio project. Sunrise, credited to the Ken Peplowski Big Band, was recorded in Union City, New Jersey on April 18 and 19, 2017 and released on Arbors in April 2018, with new charts written for the band and reworkings of older ones. Asherie plays piano throughout, alongside Nicki Parrott on bass, Chuck Redd on drums, Matt Munisteri on guitar, and a full sax and brass section that included trumpeter Jon-Erik Kellso. The following year Peplowski wrote the liner notes and produced Asherie's own Wild Man Blues (Capri, 2019), a piano trio session with Peter Washington and Rodney Green; he did not play on the record. He also recorded Duologue (2018) with the saxophonist Adrian Cunningham, and Amizade (2019), a duo album with the Brazilian guitarist Diego Figueiredo that spent fifteen weeks on JazzWeek's top fifty and toured twenty cities.

Peplowski was diagnosed with multiple myeloma in 2021, after a severe bout of COVID-19 the year before, and the illness sidelined him for roughly three years. He returned to performing and recording for a late run that his colleagues would later single out: Live at Mezzrow, taped in February 2023 at Spike Wilner's Greenwich Village club with pianist Ted Rosenthal, bassist Martin Wind and drummer Willie Jones III, was released on Cellar Music Group in July 2024. Unheard Bird, released on Arbors in April 2024, set previously unrecorded string arrangements that had been written for Charlie Parker before his 1955 death, with trumpeter Terell Stafford, pianist Glenn Zaleski, Peter Washington and Willie Jones III, strings conducted by Loren Schoenberg; Peplowski performed the book regularly at Birdland each August. He died on February 2, 2026, at 66, aboard the Celebrity Summit during a Jazz Cruise sailing in the Gulf of Mexico, five years after his diagnosis. That morning he had taken part in an on-board "Coffee Talk" with the clarinetist Anat Cohen, fielding audience questions about music and life, before retiring to rest ahead of an afternoon set. He was known among colleagues for near-total reliability, which was what made his absence from that performance immediately alarming; he was found later in his cabin. He was survived by his girlfriend, Pam Stark, his brother Ted, and his two children, Marty and Juliana, who live in Sweden.

Peplowski was, unusually among mainstream jazz clarinetists of his generation, a classically trained player first. Anat Cohen, a frequent duet partner in his final years, said his technique came from the classical tradition but was never deployed for its own sake: "He had an impeccable technique, but he never played for the sake of technique. He used it for the expression." On tenor saxophone, the instrument Benny Goodman hired him to play, he named Zoot Sims, Stan Getz and Ben Webster as his models; on clarinet, Goodman himself was the unavoidable reference point, and the British critic Russell Davies called him, without qualification, "arguably the greatest living jazz clarinetist" in a 2013 BBC broadcast. DownBeat summarized the same duality in one word, calling a 2017 performance "brilliantly entertaining," and the description held: Peplowski built a parallel reputation as a bandstand humorist, citing the New Yorker writers S.J. Perelman, James Thurber and Robert Benchley and The Jack Benny Program as touchstones, and keeping notebooks on tour to develop material between sets. He described his own aesthetic as that of an interpreter rather than a stylist, telling his own website's biography, "I consider myself an interpreter of material. If something interests me, I try to put my own spin on it, without thinking or worrying about playing in any particular style." That range let him move between a Sofia Philharmonic session, a Brazilian guitar duo, a Michel Legrand songbook, a Charlie Parker string project and a Polish-American polka inheritance without any of it reading as a detour.