Lars-Olof Danielsson was born on September 5, 1958, and grew up in Sweden's Småland province, in the small mill town of Smålandsstenar. He went to the music conservatory in Gothenburg to study classical cello, and by his own account the thing that turned him toward jazz and toward the bass was hearing the Danish virtuoso Niels-Henning Ørsted Pedersen play in concert. He never abandoned the cello. Six decades on it is still the second voice on almost every record he makes, and the habit of thinking like a cellist is the most frequently cited explanation for why his bass sound is lighter and more singing than that of most of his contemporaries.

His first decade on record was spent almost entirely inside the Swedish scene. He is the bassist on four albums by the Malmö group Mwendo Dawa for Dragon Records between 1982 and 1985, beginning with New York Lines (Dragon DRLP 41, 1982), and on the co-operative quartet record Time Unit (Dragon DRLP 69, 1984) with Anders Kjellberg, Göran Klinghagen and Anders Persson, four of whose pieces he wrote. In the same period he began a working relationship with pianist Lars Jansson that produced eight trio albums across seventeen years, from The Eternal Now (1987) to I Am That (Imogena IGCD 115, 2004), with Kjellberg on drums throughout. He also ran a fusion band of his own under the name Tiá Diá, which released two albums, Tiá Diá (1987) and Nightlight (Royal Music RMCD 043, 1990), with Peruvian drummer Alex Acuña, Lars Jansson and saxophonist David Wilczewski. The name outlived the band: his publishing company is Tia Dia Music and his studio at Mölnlycke, outside Gothenburg, is Tia Dia Studios, where a large share of his later catalogue was recorded.

The band that made his name internationally was assembled in 1985: an all-star quartet with the American saxophonist Dave Liebman on soprano, the Swedish pianist Bobo Stenson and the Norwegian drummer Jon Christensen. Their first record, New Hands, was cut at four sessions between December 17 and 20, 1985 and issued by Dragon the following year; three more followed over eleven years, Poems (Rainbow Studio, Oslo, April 1991), Far North (Rainbow Studio, February 1994, for the Norwegian label Curling Legs) and the concert document Live at Visiones, recorded on March 8 and 9, 1996 at the New York club of that name. Stenson and Christensen were both long-standing ECM artists, and the quartet's blend of that Nordic austerity with Liebman's searching soprano is the sound most listeners still identify with Danielsson's first period. Around it he made three very different leader dates: Fresh Enough (Sound On Sound, New York, January 1991), a plugged-in session produced by Niels Lan Doky with Jack DeJohnette playing on every track and John Scofield on two; Continuation (Sound on Sound, January 10, 1994) with John Abercrombie and Adam Nussbaum; and the double-CD European Voices (Swedish Radio, Gothenburg, December 1993), a nine-piece pan-European band with Michael Riessler, Marilyn Mazur, Joakim Milder, Eivind Aarset, Nils Landgren and a young Nils Petter Molvær. Abercrombie and Nussbaum returned for the trio album Origo (Waterfall Studios, Oslo, December 1995), and two Danish prize commissions put him in front of American players again: Hans Ulrik's Jazzpar Combo of 1999, recorded over three March days with Scofield and Peter Erskine, and Carsten Dahl's Jazzpar Quintet of 2000.

Two things happened in 2004 that reset his career. The first was his signing to the Munich label ACT, whose founder Siegfried Loch has produced or executive-produced nearly everything he has released since. His ACT debut Libera Me was assembled over eighteen months at six studios in three countries and set his bass and cello against the DR Danish Radio Concert Orchestra under Frans Rasmussen, with Christensen, Molvær, Liebman, Carsten Dahl and the samplist Jan Bang appearing on individual tracks. The same year he was Artist in Residence at the JazzBaltica festival at Salzau and directed its house ensemble; the open-air trio set he played there at five in the morning on July 4, 2005, with vibraphonist Christopher Dell and trombonist Nils Landgren, was released as Salzau Music on the Water.

The second was a single night in Warsaw. In July 2004 the Polish pianist Leszek Możdżer put a band together for the Jazz na Starówce festival in the Old Town and asked Danielsson to bring bass and cello. For the third chair he hired not a drummer but the Israeli frame-drum player Zohar Fresco. The one-off became a permanent group. Their first album, The Time (Outside Music OM CD001), appeared in September 2005 and eventually went Diamond in Poland on sales above fifty thousand copies, a figure almost unheard of for an acoustic jazz trio; Between Us and the Light followed in 2006, a CD and DVD box drawn from three 2005 and 2006 Polish concerts in 2008, Polska in 2013, Just Ignore It with the Dutch period-instrument orchestra Holland Baroque in 2021, recorded at Wisseloord Studios in Hilversum, and Beamo in 2024. Możdżer also became a frequent partner outside the trio, in the duo album Pasodoble (2007) and on Tarantella (2009), where Danielsson framed him with trumpeter Mathias Eick, guitarist John Parricelli and Eric Harland.

Since 2012 his main vehicle has been a band and a coinage of his own, Liberetto, a word he built from libero and libretto to describe the loose, written-through mood he wanted. The first Liberetto was recorded at Tia Dia in June 2011 with Tigran Hamasyan on piano, Magnus Öström on drums, Parricelli on guitar and Arve Henriksen on trumpet. Liberetto II (2014) kept Hamasyan and added Fresco as a guest, Liberetto III (2017) replaced him with the Martinican pianist Grégory Privat and brought in oud and English horn, and Cloudland (2021), dedicated to his ninety-two-year-old father, added the Syrian clarinettist Kinan Azmeh. Symphonized (2023) rewrote the whole book for the Gothenburg Symphony Orchestra under Peter Nordahl, and a fifth instalment, Echomyr, was recorded across two 2025 sessions and released in April 2026. Alongside it he has kept up an unusual number of parallel partnerships: the quartet 4 Wheel Drive with Landgren, Michael Wollny and Wolfgang Haffner, whose 2019 debut spent four months at number one on the German jazz chart and finished the year as the country's best-selling jazz album; a duo with the Sardinian trumpeter Paolo Fresu on Summerwind (2018); trios with Marius Neset and Morten Lund, with Iiro Rantala and Erskine, and with Jan Lundgren and Emile Parisien; and a working duo with the Danish singer Cæcilie Norby, his wife, documented on Arabesque and Just the Two of Us.

Production has been the fourth strand of the career and is not incidental to it. He produced Norby's albums from Queen of Bad Excuses (1999) onward, three records for the Korean singer Youn Sun Nah including Same Girl (2010), Viktoria Tolstoy's Pictures of Me (2006) and Rigmor Gustafsson's Alone With You (2007), and he has written and arranged for the Danish Radio orchestra, the NDR Big Band and the Gothenburg Symphony. As a sideman his most visible credits are Trilok Gurtu's The Glimpse (CMP, 1996), Tommy Smith's Azure (Linn, recorded in London in October 1995 with Kenny Wheeler and Christensen), Mike Mainieri's Northern Lights (2006) and Vince Mendoza's Blauklang (ACT, 2008), which was nominated for a Grammy in the large jazz ensemble category.

The founding fact about Danielsson's playing is that he came to the bass second, after a classical cello training, and never treated the two instruments as separate careers. He records them as a pair, often overdubbing cello lines above his own bass, and the result is a bass sound with a narrower, more vocal core than the woody thump of the American mainstream, pitched to sing rather than to propel. Niels-Henning Ørsted Pedersen was the player who converted him, and the melodic, high-register conception of the bass that the Dane made possible in Europe runs straight through his work; so does the ECM-adjacent Nordic restraint he absorbed from Bobo Stenson and Jon Christensen, both of whom he employed for two decades. What he added to it is compositional. Almost every album under his name is built from his own pieces, most of them short, modal, hymn-like and unafraid of an outright tune, and he has repeatedly rebuilt them for larger forces, first with the Danish Radio Concert Orchestra on Libera Me and later with the Gothenburg Symphony on Symphonized. The other constant is a wide, deliberately non-American palette of guests: an Armenian pianist, a Martinican pianist, a Syrian clarinettist, an Israeli frame drummer, a Jordanian oud player, a Norwegian trumpeter who plays like a shakuhachi. Critics have tended to read this as European chamber jazz, and his own coinage Liberetto, from libero and libretto, is an accurate self-description: free playing inside a written frame.