Théo De Joncker was a student of August de Boeck and Paul Gilson. For years he conducted the orchestra of the Belgian National Radio (NIR), but he also enjoyed a conducting career outside of Belgium. As a composer, he belonged to the Brussels group Les Synthétistes. This group was found by students of Paul Gilson as a way to celebrate their teacher’s 60th birthday and included Francis de Bourguignon, Théo De Joncker, Marcel Poot, Maurice Schoemaker, Jules Strens, René Bernier, and Robert Otlet.
1917 Filosofische gedachten van een draaiorgelspeler for orchestra1918 Hedda Gabler for orchestra1927 Breugeliaansche schets for orchestra1939 Sinfonia burlesca for orchestra1939 Sinfonie im klassischen Stil for orchestra1943 Symfonie nr.3 for orchestra1944 Muzikaal portret van Bernard Shaw for orchestraAllegro for chamber orchestraBoere-Charleston for tenor and orchestra - text: Paul van OstayenCello Concerto for cello and orchestraDe laatste oogenblikken van Lodewijk XI for small orchestraDon Quichotte rêve... for orchestraFantasia - Serenata for flute and orchestraHistoriette pour bébé for stringsIntroduction et rondo capricio for bassoon and orchestraLe glas for orchestraRapsodie vénézuélienne for orchestraSérénade for violin and orchestraSymfonische proloog for orchestraVlaamse dans I for orchestraBrassband works
Chant mystique, for brass bandCharles Stratton, comical fairytale for brass bandDeux Extraits du Jardin des Supplices, based on a novel by Octave MirbeauGamineries - Guitenstreken, for brassbandMarche, for brassbandPolomé, for brassbandFor Paul Gilson, for brassbandAch, mijn bietje, jij zingt zo schone for mixed choir and piano - text: Guido GezelleAnneessens for mixed choir and piano - text: Frans de CortDaer ging een pater langs het land for male or female choir and pianoDe mei for choir a cappella - text: G. W. LoovendaelDe pen for mixed choir and piano - text: Jan A. Van DroogenbroeckDes winters als het reghent for male or female choir and pianoMinnekepoes for choir a cappella - text: Jan A. Van Droogenbroeck1917 Conte pour quatuor for flute, oboe, clarinet and bassoon1917 Novelette pour trio for flute, oboe and viola1938 Drie vertelseltjes for oboe, clarinet, bassoon and horn1963 Concerto for flute, oboe, clarinet, bassoon and horn in FPrélude for oboe, clarinet, bassoon and hornQuintette for flute, oboe, clarinet, horn and bassoon1927 Verselets à mon premier né for tenor and orchestra - text: Clotilde de Surville1938 De messias for Recitant and piano - text: Dirk VansinaDe Vlaming staat zijn eigen taal en zeden af for mezzo-soprano and orchestra - text: Guido GezelleDe wilde jacht for mezzo-soprano and orchestra - text: Willem GijsselsEerste boek van Schmol for middle voice and orchestra - text: Paul van OstayenHei da lieve dreupel water for mezzo-soprano and orchestra - text: Guido GezelleHet meezennestje for soprano and orchestra - text: Guido GezelleHet zonnelied van Achnaton for Recitant and piano - text: J. CoutrijnMorgenstond for alto and orchestra - text: Guido GezelleO Mocht ik for mezzo-soprano and orchestra - text: Guido GezelleSlaapt, slaapt, kindje slaapt for soprano, mixed choir and piano ad. libitum - text: Guido GezelleStilleven for mezzo-soprano and orchestra - text: Staf Van der LooTot de Mane for mezzo-soprano and orchestra - text: Guido GezelleWinden gingen te rust for mezzo-soprano and orchestra - text: Wies MoensWintermuggen for soprano and orchestra - text: Guido GezelleZonnezoen for soprano and orchestra - text: Jef Mennekens1915 Le chien qui lache sa proie pour l'ombre1915 Le renard et les raisinsEille - WalsjeEsquisse sur le nom "ANNA"GaminerieIl s'éveille.PianowerkenPièce pour piano sur le nom de FauréVlaamse dans