Boesmans was born in Tongeren and studied piano at the Conservatory in Liège, where he was also introduced to serial composing techniques by Pierre Froidebise. However, it was only after coming into contact with the "Liège Group" (Henri Pousseur, André Souris, and Célestin Deliège) in 1957 that he began to write music, as a self-taught composer. Starting in 1962 he participated in productions of the Centre de Recherches Musicales de Wallonie, collaborating with Pousseur. He was also active as a pianist with the Ensemble Musique Nouvelle. Also in 1962 he became a producer at the Radio Télévision Belge de la Communauté Française (RTBF), working with the radio orchestra there. From this experience he learned much about composing and orchestrating music. Recognition quickly followed, and in 1971 he won the Prix Italia for his composition Upon La-Mi (Visscher 2001).
He still works as a producer for the RTBF and is composer in residence at the La Monnaie opera house in Brussels.
- La Passion de Gilles (1983) Libretto by Pierre Mertens (Morris 1996,[page needed])
- Reigen (1993); based on La Ronde by Arthur Schnitzler. Review in Le Monde pronounced it "the greatest opera of the last 75 years."[full citation needed]
- Wintermärchen (1999); based on The Winter's Tale by William Shakespeare.
- Julie (2005); based on Miss Julie by August Strindberg.
- Yvonne, princesse de Bourgogne (2009); based on Iwona, księżniczka Burgunda by Witold Gombrowicz.
- Poppea e Nerone (2012); New orchestration, for a modern chamber orchestra, of Monteverdi's L'Incoronazione di Poppea'. First performed at Teatro Real in Madrid, conducted by Sylvain Cambreling and directed by Krzysztof Warlikowski.
- Violin Concerto (1980)
- String Quartet No.1 (1988)
- Surfing for viola and orchestra (1990)
- Love and Dance Tunes for baritone and piano (1993); settings from Shakespeare's sonnets
- Summer Dreams, String Quartet No.2 (1994)
- Trakl Lieder; String Quartet [No. 1]; Surfing. Françoise Pollet (soprano), Orchestre du Théâtre Royal de la Monnaie, conducted by Sylvain Cambreling; Arditti String Quartet; Christophe Desjardins (viola), Ensemble Musique Nouvelle, conducted by Georges Elie Octors. Trakl Lieder recorded live, Palais des Beaux-Arts, Brussels, 14 April 1990; String Quartet recorded at the Royal Conservatory of Liège, 24 March 1990; Surfing recorded at the Palais des Beaux-Arts, Brussels, 4 June 1990. CD recording, 1 audio disc: digital, 12 cm, stereo. Ricercar RIC 083065. Anloy: SPRL Ricercar, [n.d.].
- Reigen. Cypres.[full citation needed]
- Wintermärchen. DG.[full citation needed] Sung in German, in scene four the language changes from German to English and Boesmans introduces AKA Moon, a jazz/funk group.
- Julie. Garry Magee, Malena Ernman, Monnaie Chamber Orchestra, Kazushi Ono. CD recording. Cypres (CYP4626), 2005. Video recording, DVD. Garry Magee, Malena Ernman, Kerstin Avemo, Monnaie Chamber Orchestra, Kazushi Ono. BelAir, 2005.
- Yvonne, princesse de Bourgogne. Opéra National de Paris Mireille Delunsch and Yann Beuron. Cypres[full citation needed], 2011 Klangforum Wien, Sylvain Cambreling.
- Julie. Garry Magee, Malena Ernman, Kerstin Avemo, Monnaie Chamber Orchestra, Kazushi Ono. DVD recording. BelAir, 2005.
- Morris, Mark. 1996. "The Opera La passion de Gilles (1983) Is a Dark Story of Perversion, Malice, and Child Abuse, Set in the 15th Century and Providing a Commentary on the Present Day. Its Colours Are Dark, Intense, and Sparse, in Keeping with the Subject". In A Guide to 20th-Century Composers.[full citation needed]
- Visscher, Eric de. 2001. "Boesmans, Philippe". The New Grove Dictionary of Music and Musicians, second edition, edited by Stanley Sadie and John Tyrrell. London: Macmillan Publishers.