Motoharu Yoshizawa (吉沢元治) was born on 30 April 1931 in Hino, on the western edge of Tokyo, and graduated from Chuo University. Japanese reference works list him as both a jazz bassist and a jazz cellist, and give 1960 as the year he turned professional. Discogs and English Wikipedia add that he played in straight-ahead groups through the 1960s, among them Jun Yoshiya's group and the quintet of the clarinettist Eiji Kitamura, and that he sat in with Elvin Jones at Pit Inn in 1966, during John Coltrane's tour of Japan. His earliest documented session is a Victor LP from the outdoor Karuizawa Newtown jazz festival of 2 to 4 August 1963, on which he plays bass on two tracks. English Wikipedia also places his first free-style playing in the mid-1960s, in groups with the pianist Yosuke Yamashita and Kazunori Takeda.

In 1968 he formed a trio with the saxophonist Mototeru Takagi and the drummer Sabu Toyozumi, a group that a Jazz Tokyo reviewer calls the one most often named as Japan's first free jazz band. Nothing by that trio was recorded. What survives from the same months is the work he did in other people's bands. On 23 May 1969, at Tokyo Studio Center, he played bass and cello on Masahiko Togashi's We Now Create, a quartet date with Masayuki Takayanagi on guitar and Takagi on tenor saxophone and corn pipe. On 18 September 1969 he recorded Independence: Tread On Sure Ground with Takayanagi's New Direction trio at Teichiku Kaikan Studio, credited for bass, cello, percussion and folk pipe, with Toyozumi on drums. The trio played Station '70 in Tokyo on 11 and 12 March 1970, and the two nights were issued by P.S.F. Records in 1994 and 1995 as Call in Question and Live Independence. On 9 October 1969 he and Takagi played a duo at the Shinjuku club Nagisa, which P.S.F. released in 1994 as Shinkai (Deep Sea), with readings of Ornette Coleman's "Lonely Woman" and Togashi's "Four Units" alongside Takagi's own title piece.

The solo bass records started in the early 1970s. The English Wikipedia entry dates his first solo bass performance to 1969, in step with the experiments of Barre Phillips in Europe, and the Japanese reference work says 1970. The first release was a duo, though: on 30 November 1973 he recorded Dreams with the American pianist Dave Burrell at Iino Hall in Tokyo, a two-side LP for Trio Records whose second side is a long reading of Billy Strayhorn and Duke Ellington's "Daydream." On 13 September 1974 he gave a bass solo recital at Yasuda Seimei Hall in Shinjuku, issued by Trio as Inland Fish; on its closing piece, "Correspondence," Toyozumi joins on percussion. The concert was produced by the critic Aquirax Aida, the figure behind most of the Tokyo free-jazz documents of the decade. In July 1975 Yoshizawa recorded ten pieces at a church in Karuizawa for the ALM label, Cracking Mirror and/or The Fossil Bird: Bass Fragments. He wrote the sleeve notes himself and dedicated pieces to Steve Lacy, Barre Phillips and Aida. On 29 September 1975 his second solo concert at Aoyama Tower Hall became Outfit: Bass Solo 2½, completed with one studio track cut on 7 November.

Lacy was in Tokyo that June. On 7 June 1975, at Nippon Columbia's 1st Studio, Yoshizawa played bass on the soprano saxophonist's album Stalks, with Togashi on percussion. Eleven days later, on 18 June, he was one of the bassists in Lacy's sextet for The Wire, with Masahiko Satoh on piano, Yoshio Ikeda on bass, Keiki Midorikawa on cello and bass, and Togashi again. Steve Lacy is profiled on JazzProfiles.com.

October 1975 was his busiest stretch with the alto saxophonist Kaoru Abe. They had already played a duo at the Passe-Tamps cafe in Fukushima on 11 March 1974, and Yoshizawa recorded a solo set there on 12 October 1975. On 15 and 18 October, at Iruma Civic Hall and Aoyama Tower Hall, Aida organised the two concerts that became Nord: Duo '75, issued by ALM in 1981. Yoshizawa plays bass on two of the three improvisations and cello on the other. In 1978 Aida brought the English guitarist Derek Bailey to Tokyo. On 3 March, at Kavalika in Machida, Yoshizawa played with Abe, Bailey and the trumpeter Toshinori Kondo, a concert released in 1999 as Aida's Call; Abe, Kondo and Yoshizawa without Bailey are on a cassette from the same night, 78.3.3. On 19 April, at Polydor's 1st Studio, he joined Bailey and the percussionist Toshi Tsuchitori for two trio improvisations on Bailey's Duo & Trio Improvisation.

The 1980s were quieter on record and busy in clubs. Oops! (1980), a duo LP with the saxophonist Takao Haga pressed in 100 copies, was recorded live in March and May 1980, with Yoshizawa on cello, bass, voice, organ and assorted objects. In London during Company Week, between 29 June and 3 July 1982, he played bass on the Incus double album Epiphany alongside Bailey, Fred Frith, George Lewis, Keith Tippett, Julie Tippetts, Ursula Oppens, Anne LeBaron, Philipp Wachsmann and Akio Suzuki. Kozan (Tiara, 1986) is a trio with the guitarist Hirokazu Yamada and Takagi, recorded on 31 October 1985. On 8 July 1987 he and Takagi played a duo at the Galerie de Cafe Den in Setagaya, and on 23 August 1989 he played a solo concert in the same room; both were issued in 2022 on the three-CD set Duo & Solo.

He spent roughly six months in New York in 1989 and 1990. The recordings made there came out on P.S.F. as Gobbledygook: a duo with the percussionist Ikue Mori at the Whitney Museum on 27 June 1990, a trio with the cornetist Butch Morris and the guitarist Elliott Sharp at the Knitting Factory on 22 May, and a duo with Sharp at P.S. 122 on 28 June. The same label's boss, Hideo Ikeezumi, then documented him repeatedly. Back in Tokyo he recorded Heisei Live! (1990) with the singer Kan Mikami and the guitarist Keiji Haino, Angels Have Passed (recorded at Shinjuku Pit Inn on 13 October 1991) with the violinist Takehisa Kosugi and the pianist Haruna Miyake, and From the Faraway Nearby (28 to 30 November 1991), whose credits name his homemade five-string bass, the "Tiritack." He also appears on several records by the singer Kazuki Tomokawa for P.S.F. between 1993 and 2004.

From 1993 his regular stage was Cafe Amores in Hofu, Yamaguchi, where the promoter Takeo Suetomi recorded him. He played a duo with the Korean percussionist Kim Dae Hwan there on 8 September 1993, issued by NoBusiness in 2025 as Way of the Breeze. Empty Hats is a solo set from 24 February 1994. On 5 April 1994 he played a duo with Barre Phillips, released in part in 1998 as Live "Okidoki" and in 2018 as Oh My, Those Boys!; Phillips and Yoshizawa recorded Uzu together on 8 February 1996. On 29 April 1996 he played a duo with the saxophonist Evan Parker there, issued in 2015 as Two Chaps, and Parker's Leo Records set Synergetics: Phonomanie III also features him on bass and voice. Play Unlimited was recorded at Shibuya Apia on 12 May 1997 and dedicated to "comrades who fell along the way."

His last solo concert took place at Shibuya Apia on 28 November 1997 and was released on video as It's a Day. On 7 August 1998 he played with the Tokyo band Gyaatees at La-Mama in Shibuya; that set came out as Welcome: Motoharu Yoshizawa Last Live. He passed away on 12 September 1998, aged 67. Since then the archive has kept opening: the Aida's Call CD in 1999, Two Chaps in 2015, Oh My, Those Boys! in 2018, Duo & Solo in 2022 and Way of the Breeze in 2025. English-language writing on him was long limited to a memorial piece in the magazine Halana, and Soejima Teruto's Free Jazz in Japan: A Personal History covers the scene he belonged to.

Yoshizawa is best known as a solo bassist, and the solo work is where his sound is easiest to follow. The 1975 Cracking Mirror LP is made of ten pieces with titles ("Soft Nothings," "Hiccups," "Distance"). The later P.S.F. records are different: Empty Hats is five untitled tracks between ten and twenty minutes, From the Faraway Nearby and Gobbledygook use no track titles at all, and Play Unlimited is four numbered "Music" pieces, one of them over thirty minutes.

From the early 1990s he played a bass of his own design. Discogs credits describe it as a homemade electric vertical five-string bass, and the sleeve of From the Faraway Nearby gives its name as the "Tiritack." A Jazz Tokyo reviewer describes his later method as contrabass with effects units, mixing the unprocessed bass sound with processed sound, and calls it unlike anyone else's. The same writer notes that he worked mainly alone and did not belong to a scene or circle. English Wikipedia calls him a pioneer of solo bass performance, working in parallel with Barre Phillips; the two are often paired, and they recorded together in 1994 and 1996.

He did not stay inside any one idiom. He played cello as well as bass; he took Ornette Coleman's "Lonely Woman" and the Ellington-Strayhorn "Daydream" into free playing in 1969 and 1973; he played behind the folk singer Kan Mikami and the guitarist Keiji Haino in 1990 and on a run of records by the singer Kazuki Tomokawa; and he worked with players from Europe, Korea and the United States as readily as with Japanese ones. The through line in the credits is Aida's concert circuit, the Pit Inn and Cafe Amores audiences, and the P.S.F. label, which issued most of his late catalogue.