Diderik Wagenaar was born on May 10, 1946 in Utrecht. He has lived and worked all his adult life in The Hague.
Born to a musical family that includes Johan Wagenaar, he began playing piano at the age of eight and by the time he was fourteen had set his sights on a musical vocation. As a teenager in the early 1960s he loved Renaissance music, Bach, Ravel, and Thelonious Monk; at the age of eighteen he began studying music theory with Jan van Dijk, Hein Kien and Rudolf Koumans and piano with Simon Admiraal at the Royal Conservatory in The Hague. After having completed his studies, he followed analysis classes with Kees van Baaren that fostered his interest in composing.
In the 1970s, together with Louis Andriessen and Gilius of Bergeijk, Wagenaar initiated the Digilou trio, a trio that combines improvisation and composition elements; Diderik’s composition Praxis (1973) for two pianos and oboe is a result of this composition style. In 1973, the trio stopped this cooperation. Since 1969, Wagenaar has taught music theory and 20th century music at the Royal Conservatory in The Hague. In 1990, he began to teach composition also at the Royal Conservatory, and a few years after that he began to give instrumentation lessons as well.
As a composer, Wagenaar is essentially self-taught. It was during his student years in the mid-60s that Wagenaar began to develop as a composer. Although fascinated by the concerts given by Pierre Boulez and Bruno Maderna with the Hague Philharmonic, he admits to having "no real grip" at that time on the musical avant-garde, and began to look around for other starting-points for his own music. In addition to his fascination with jazz, an important encounter at that time was with the music of Charles Ives, which taught him the value of inclusiveness. It also encouraged his tendency to attempt a synthesis between tonality and atonality, to connect previously disparate systems of musical thought. Today Wagenaar feels that the notion of a "music of inclusion" can be seen as an important aspect of the new Dutch music as a whole.
Though Wagenaar's ideas may be complex, they are always presented in a clear and straightforward manner. His influences include Stravinsky, a key figure for the composers of the Hague school, but also importantly Monk and John Coltrane.
Wagenaar's major works include Praxis (1973) for two pianos; Liederen (1976) for wind band; Tam Tam (1978) for the Hoketus Ensemble; Metrum (1984) for large orchestra and saxophone quartet; Solenne (1992) for six percussionists; Galilei (1999) for orchestra and chorus and Tango Waltz for orchestra (2004). Some of his works are commissions for the ensembles Orkest de Volharding, Hoketus, Slagwerkgroep Den Haag and Icebreaker and for the Concertgebouw Orchestra.
In April 1989 Wagenaar received the Kees van Baaren Prize for his piece Metrum. In 1996 he was awarded the Matthijs Vermeulen Prize for his Trois poèmes en prose (1995). Additionally, Diderik Wagenaar was a guest of honor during the Bang on a Can Marathon in 2001 in New York.