Niels-Henning Ørsted Pedersen, known throughout jazz as NHØP, was born on May 27, 1946, in Osted, near Roskilde on the Danish island of Zealand, the youngest of five children. His mother had all of her children study music, and he began on piano; he took up the double bass at 13 because his older siblings already played other instruments and the family could use a bassist. At 14 he was working professionally in Copenhagen, first in the Jazz Quintet 60 (Jazzkvintet 60), a group with pianist Bent Axen, trumpeter Allan Botschinsky, tenor saxophonist Niels Husum and drummer Bjarne Rostvold. He made his debut at the Jazzhus Montmartre on New Year's Eve 1961, at 15, and soon belonged to the club's house rhythm section, which accompanied the American soloists who came through Copenhagen.

That club was his training ground. In 1962, still 15, he was the bassist for Bud Powell's seven-week engagement at the Café Montmartre, and on April 26, 1962, he recorded the trio album Bouncing with Bud with Powell and the drummer William Schiøpffe. On January 14, 1963, he took part in Albert Ayler's Copenhagen session My Name Is Albert Ayler, and in October 1963 he was one of two bassists on Rahsaan Roland Kirk's Kirk in Copenhagen, with the Spanish pianist Tete Montoliu. When Kenny Drew settled in Copenhagen in 1964, Drew, Pedersen and the drummer Alex Riel became the Montmartre's regular rhythm group, and Pedersen was also the bassist on Dexter Gordon's One Flight Up, recorded in Paris on June 2, 1964, with Donald Byrd and Drew. Through the 1960s he played with Ben Webster, Brew Moore, Don Byas, Stuff Smith, Sonny Rollins, Dizzy Gillespie and Jackie McLean. In the autumn of 1965 he toured Europe with pianist Bill Evans, with drummer Alan Dawson and, on some dates, the alto saxophonist Lee Konitz. He was also a member of the Danish Radio Big Band from 1964 to 1982. Twice he was offered a place in Count Basie's orchestra: he declined the first offer at 17 because he was too young to get a work permit in the United States, and the second after he was told at the American embassy in Copenhagen that permanent residency could expose him to the draft for the Vietnam War.

His best-known association began in 1972, when he joined the trio of pianist Oscar Peterson, a partnership that lasted until 1987. Peterson later wrote that after hearing Pedersen he wanted to play with him and invited him to join his trio in the early 1970s, and Ray Brown, Pedersen's predecessor on bass, regarded the Dane as the only upright bassist who could keep pace with the pianist. With guitarist Joe Pass in the group, the trio recorded The Trio live at Chicago's London House in 1973 for Norman Granz's Pablo label; it won the Grammy Award for Best Jazz Performance by a Group. Pedersen became a house bassist for Pablo. At one Montreux festival in the 1970s he took part in seven live albums over two days, working with Basie, Dizzy Gillespie, Milt Jackson, Harry Edison, Benny Carter and Peterson, and he recorded with Ella Fitzgerald on Digital III at Montreux (July 12, 1979) and on Nice Work If You Can Get It with André Previn (1983). With Pass he made two duo albums, Chops (recorded in London on November 19, 1978) and Northsea Nights (the North Sea Jazz Festival, July 1979), and he joined Pass and Stéphane Grappelli on the live Tivoli Gardens, Copenhagen, Denmark (July 6, 1979). By the time he left Peterson he had appeared on about 400 albums, according to The Independent's obituary.

Under his own name and in duos and trios he built a large catalogue, much of it for the Copenhagen label SteepleChase. With Kenny Drew he recorded more than 50 albums in duo and trio settings, beginning with Duo (April 2, 1973) and Duo 2 (1974), and he made duo albums with Paul Bley (1973), Archie Shepp (Looking at Bird, recorded February 7, 1980), Martial Solal, Tete Montoliu and the guitarist Philip Catherine. His leader dates include Jaywalkin' (1975, with Catherine, drummer Billy Higgins and pianist Ole Kock Hansen), Double Bass (1976, with Sam Jones), the Montmartre trio albums with Catherine and Billy Hart (recorded October 2 and 3, 1977), and Dancing on the Tables (1979), a quartet with David Liebman, John Scofield and Hart. He had a particular gift for Danish songs and folk melodies, which he arranged for jazz settings, and The Eternal Traveller (recorded in Copenhagen in 1984) pairs Danish themes with Paganini transcriptions and a nursery rhyme sung by two of his daughters. His own compositions include "My Little Anna," "Jaywalkin'" and "The Puzzle."

In his later decades he turned increasingly to European partners: trumpeter Palle Mikkelborg and keyboardist Kenneth Knudsen (Heart to Heart, 1986), the Danish Radio Big Band (Ambiance, 1994), and, on two Verve albums in 1996 and 1998, both with guitarist Ulf Wakenius, the second with Phil Woods and Peterson as guests. Friends Forever, recorded in Copenhagen in August 1995 with pianist Renee Rosnes and drummer Jonas Johansen, was a tribute to Drew, who had died in 1993. In 1999 he began a duo with pianist Mulgrew Miller, which toured Europe, Japan, Australia and Korea and later became a trio with drummer Alvin Queen; that group stayed together until his death. He taught at the Rytmisk Musikkonservatorium in Copenhagen. DownBeat's critics named him best bassist in 1981, and he received the Nordic Council Music Prize in 1991. Niels-Henning Ørsted Pedersen passed away on April 19, 2005, at 58, of heart failure, with his wife, Solveig, and their three children at his side. A memorial album, Friends Forever, appeared the same year, and the live set The Unforgettable NHØP Trio Live (2007) includes a concert in Hamburg recorded on March 11, 2005.

Pedersen combined a big, rich sound with speed and melodic imagination. The Guardian likened his right hand to a finger-style guitarist's: he plucked with three or four fingers rather than the one or two most bassists use, which let him walk lines at very fast tempos and keep up with Oscar Peterson, one of the fastest pianists in jazz, even in drummerless duos. He also played with a strong bow technique. A pianist in his first years, he described his aim as communication, saying that a bassist always works behind the music and not in front of it. His influences included Walter Page, Paul Chambers, Scott LaFaro and Ray Brown, and he used the same instrument from 1963 onward. Though he was most often heard in standards, blues and swing, he was equally comfortable in the open settings of Archie Shepp and Albert Ayler, in Danish song, and in classical material such as the Paganini pieces on The Eternal Traveller. His influence is visible in later bassists: Lars Danielsson says hearing him in concert led him to the instrument, Jesper Bodilsen studied with him, and Martin Wind names him among his models.