Pekka Kuusisto was born in Espoo on October 7, 1976, into a family of Finnish composers. His grandfather Taneli Kuusisto was a composer and organist, his father Ilkka Kuusisto composed operas and directed the Finnish National Opera, and his mother taught music. His older brother Jaakko Kuusisto (1974 to February 23, 2022) was a violinist, composer and conductor, and the two brothers co-directed the chamber music festival at Lake Tuusula from 1999 to 2006, after which Pekka continued alone.

He started the violin at three with Géza Szilvay at the East Helsinki Music Institute, entered the Sibelius Academy in 1983, and from 1985 studied there with Tuomas Haapanen. From 1992 to 1996 he studied with Miriam Fried and Paul Biss at the Indiana University School of Music. In 1992 he placed third at the Carl Nielsen competition, and in 1995, at 19, he became the first Finn to win the International Jean Sibelius Violin Competition, which also gave him a special prize for the best performance of the Sibelius concerto. His first record, the Sibelius Violin Concerto with the Helsinki Philharmonic under Leif Segerstam, appeared on Ondine in 1996.

Kuusisto is a classical violinist with a documented jazz side, and the proportions matter. AllMusic lists his genres as Classical and Folk, English Wikipedia opens by calling him a classical violinist and composer, and nearly everything in his catalogue is concertos, chamber music and new commissions. The jazz connection is real and specific rather than incidental: AllMusic's biography says he plays jazz with the trio Töykeät, and his recurring jazz partner since the late 1990s is the Finnish pianist Iiro Rantala, who was the pianist and main composer of that trio.

The first documented meeting on record is Sisu (EmArcy, 1997), Töykeät's major-label album, on which Pekka is a featured violinist on four tracks (3, 5, 9 and 11) and Jaakko on four others (5, 7, 9 and 11). Track 3 is Rantala's arrangement of a Sibelius song. The collaboration grew into Music! (BIS, 2002), recorded in January 2001 at the Sibelius Hall in Lahti with the Lahti Symphony Orchestra under Osmo Vänskä. The Kuusisto brothers, the trio of Rantala, bassist Eerik Siikasaari and drummer Rami Eskelinen, and the orchestra play twelve tracks of music by Rantala, Jaakko and Pekka himself, including Rantala's "Waltz for Michel Petrucciani" (Michel Petrucciani was the French pianist). Pekka is the electric violinist, sings on "Tango Ouh," and wrote three short "Snack" pieces for violin and loop programming, each with a different partner from the trio (bass, piano and drums). Töykeät disbanded in 2008.

In 2009 Kuusisto and Rantala made a duo album, Subterráneo (Liverace), seven tracks arranged by both men in a tango idiom, with Rantala on piano, upright piano and a nail piano. The pair kept playing together as a recital duo: on July 23, 2012 they gave a programme at the Concertgebouw in Amsterdam that included Rantala's "Uplift" and Bernstein's "Maria," and English Wikipedia lists Rantala among his recital partners alongside Anne Sofie von Otter, Angela Hewitt, Kimmo Pohjonen and Nicolas Altstaedt.

Outside the Rantala axis he crosses idioms without settling in any of them. He leads the folk group The Luomu Players (Folk Trip, Ondine, 2002), co-leads the duo Kraft with accordionist Johanna Juhola, wrote the music for Paula Vesala's songs on Kiestinki (2011), and has been a guest violinist for Nightwish, the metal band Mokoma, the electronic group RinneRadio, the hip hop and electronic band Don Johnson Big Band and the guitarist Jarmo Saari. With Samuli Kosminen he wrote the score for the animated series Moominvalley (2019), which also has a soundtrack album credited to Kosminen, Kuusisto and Jarmo Saari. Alongside this he was artistic partner of the Tapiola Sinfonietta from 2006 to 2013, artistic director of the ACO Collective of the Australian Chamber Orchestra from 2016, and in August 2021 became artistic director of the Norwegian Chamber Orchestra, which he leads from the violin. First Light (Pentatone, 2021), with that orchestra and music by Nico Muhly and Philip Glass, and Willows (Platoon, February 20, 2026), with the singer and guitarist Sam Amidon and the same orchestra, are two recent albums. His honours include the Tanner Prize in 2008, the Nordic Council Music Prize in 2013, the Pro Finlandia medal in 2016 and the Finnish State Music Prize in 2024.

English Wikipedia credits his classical work with a fresh approach to the repertoire and a strong commitment to new music; the jazz-adjacent side of his work shows up as improvisation, electric violin and live electronics rather than as swing or bebop vocabulary. On Music! he plays electric violin and builds his own loop-based pieces, and in recital he has paired Bach's D minor Partita with electronic improvisations on funeral chorales. AllMusic names the experimental saxophonist and composer John Zorn as an artist he admires, and quotes him telling the Guardian that the ability and desire to improvise has turned out to be one of the best things he has.

The jazz he plays comes through Finnish musicians rather than through the American tradition: Töykeät, whom English Wikipedia describes as a jazz trio running from humorous ragtime to sentimental waltz, and Rantala, one of the best known Finnish jazz pianists. The repertoire with Rantala is tango, waltz and Finnish popular song re-harmonised and extended, which sits closer to crossover and third stream than to straight-ahead jazz. Finnish folk music is a second influence, and English Wikipedia notes that his approach to the violin changed substantially once he became more involved with folk music and its players. Taken as a whole, he is a classical soloist and director whose jazz output is a small, well-documented part of a much larger catalogue.