Nils Lennart Landgren was born on February 15, 1956, in Degerfors, in the Swedish province of Värmland, into a musical family; his father played jazz cornet. He started on drums at six and switched to trombone at thirteen. From 1972 to 1978 he studied classical trombone at the music school in Karlstad and then in Arvika, where he met the folk-jazz pioneer Bengt-Arne Wallin and the trombonist Eje Thelin, who persuaded him to leave a strictly classical path for improvisation. He moved to Stockholm as a working trombonist and soon toured with the pop singer Björn Skifs, whose band Blue Swede had topped the American pop chart with "Hooked on a Feeling." In 1981 Thad Jones invited him to join his big band Ball of Fire as lead trombonist. By his own count he has played on at least 500 albums, among them recordings by ABBA, The Crusaders, Eddie Harris and Herbie Hancock.

His own records began in the mid-1980s with Planet Rock and Streetfighter (both 1984) and You're My Number One (1985), all on Swedish labels. From 1985 to 1987 he also appeared in more than 360 performances of the stage play Skål, as actor, singer, trombonist and dancer. Miles from Duke (1986), recorded in October 1985 with Wallin and a big band, won the Swedish Grammophone Prize. The duo records Chapter Two with the guitarist Johan Norberg, Follow Your Heart (1990), Untitled Sketches (1991, with the Polish trumpeter Tomasz Stańko), Red Horn (1992) and Ballads (1993) followed; from the last of these, German Wikipedia says, he concentrated on ballad singing alongside the trombone.

The band that carried him abroad began as the Nils Landgren Unit in 1992. After its appearance at the JazzBaltica festival in Salzau, Germany, in 1994 it became the Nils Landgren Funk Unit, and the live album Live in Stockholm (recorded in 1994, issued by ACT in 1995), with Maceo Parker as a guest, led to a long relationship with the Munich label ACT and its founder Siegfried Loch. Paint It Blue (1996), a tribute to Cannonball Adderley with the Funk Unit's bassist Lars Danielsson and keyboardist Esbjörn Svensson and guests including Michael Brecker, Randy Brecker and Till Brönner, won the German Jazz Award. Live in Montreux (1998) and 5000 Miles (1999, with Esbjörn Svensson on keyboards and Roy Hargrove as a guest) were followed by Funky ABBA (2004), built on the Swedish group's songs. The band has kept recording for ACT since: Licence to Funk (2007), Funk for Life (2010), which supported a music project for children in the Kibera district of Nairobi, Teamwork (2013, with Joe Sample and Wilton Felder of The Crusaders), Unbreakable (2017, with Ray Parker Jr.), Funk Is My Religion (2021) and Raw: Celebrating 30 Years (2024).

A second line of work is quieter and more Nordic. With the pianist Esbjörn Svensson he made two duo albums of Swedish folk songs, Swedish Folk Modern (recorded August 1997, released 1998) and Layers of Light (recorded December 2 and 3, 1999, in Oslo, released 2001); ACT's notes say the pair were inspired by their former teacher Wallin's 1962 album Old Folklore in Swedish Modern and were continuing what Jan Johansson's Jazz på svenska and Wallin had started in the early 1960s. He also made Gotland (1996) with Stańko, the vocal albums Sentimental Journey (2002) and I Will Wait for You (2003, with the singer Rigmor Gustafsson and the Fleshquartet), Creole Love Call (recorded in New Orleans in May 2005) with Joe Sample, Ray Parker Jr. and a local rhythm and brass section, and since 2006 the Christmas with My Friends series, a holiday concert tour and album with Scandinavian singers that has reached nine volumes through 2025. Among his larger projects are The Moon, the Stars and You (2011), with guests including Steve Gadd, Richard Galliano and Joe Sample and, on one track, the Stockholm Philharmonic, Some Other Time (2016), a Leonard Bernstein tribute with the singer Janis Siegel, the pianist Jan Lundgren, arrangements by Vince Mendoza and the Bochum Symphony Orchestra, Kristallen (2020), a duo album with Lundgren, and the quartet 4 Wheel Drive with the pianist Michael Wollny, Lars Danielsson and the drummer Wolfgang Haffner, whose albums appeared in 2019 and 2023.

He has also held leading posts in German jazz. He was a member of the NDR Big Band in Hamburg from 1998 to 2001, was artistic director of the Jazzfest Berlin in 2001 and again from 2008 to 2011, and has directed JazzBaltica since 2012; the festival's 2026 programme, for its edition of June 25 to 28, still lists him as artistic director. According to German Wikipedia he began teaching jazz trombone at the Hamburg University of Music and Theatre in 2006 and became a professor there in 2014. He has produced albums for the singers Viktoria Tolstoy and Ida Sand and for Wolfgang Haffner, among others. His honors include the German Jazz Award (for Paint It Blue), the Tore Ehrling Prize (2002), an honorary doctorate from Karlstad University (2008), membership of the Royal Swedish Academy of Music (2011), the Sir George Martin Music Award (2012), the Jazzkatten Golden Cat (2015), the Joachim-Ernst-Berendt honorary prize of the city of Baden-Baden (2016), the Order of Merit of the Federal Republic of Germany (2019), the Rheingau Music Prize (2021) and the Order of Merit of Schleswig-Holstein, presented in Kiel on February 11, 2025. He turned 70 on February 15, 2026. His recent releases are A Letter to Eje Thelin (Prophone, November 2025), on which he is the trombone soloist with the Göteborg Jazz Orchestra, Love of My Life (ACT, 2026), recorded live at Berwaldhallen in Stockholm with the Swedish Radio Symphony Orchestra and arrangements by Vince Mendoza, and the live set Jazz at Berlin Philharmonic XIX: Nils Landgren 70, released on August 28, 2026.

Landgren is known as "Mr. Red Horn" and "The Man with the Red Horn" for the red Yamaha trombone he plays, and he moves between jazz, funk, soul, pop songs and Swedish folk and Christmas material. His Funk Unit works in the funk and soul jazz tradition of The Crusaders and Cannonball Adderley, whom he honored directly on Paint It Blue; AllMusic lists his styles as post-bop, hard bop, jazz-funk and soul jazz. His duo records with Svensson set old Swedish melodies plainly, without a large conceptual frame, in a way ACT places in the line of Jan Johansson and Wallin, and his vocal albums are mostly ballad sets. Wallin and Thelin, whom he met as a student, turned him from classical study toward improvisation, and his early years as a studio and pop-tour trombonist, including the ABBA work, came before the jazz career described above. German Wikipedia calls him one of the most successful European jazz musicians, and AllMusic calls him a prolific Swedish jazz trombonist. Much of his catalog, including the Christmas albums and the pop-song projects, sits outside straight-ahead jazz; his standing as a jazz musician rests on the Funk Unit, the duo and quartet records, his big band work and his German festival and teaching posts.