We do not know, but we assume that he has musically grown up within the church.
probably lived and worked between 1160-1180 in Paris at the Notre Dame Cathedral with other composers
Leoninus (12th century)
Leoninus' oeuvre contains:
organa dupla (two-part compositions based on a cantus firmus with a religious text in the lowest voice, the tenor)
Two-part organum in discantus style: note against note or a homorhythmical style (diaphonica organica). Cantus firmus = gregorian chant in the lowest voice.
Two-part organum with vox principalis in the lowest voice in long notes (based on a gregorian melody) and a faster moving, improvisation-like vox organalis, i.e. short note values (diaphonica basicilica; it has the same features as the older St. Martial style)
Both styles can be found within one composition. The rhythmic organization of his works is probably free. Hence the qualification of his style as 'ornamental'.
Well known composition: Viderunt omnes with a short section in discantstyle (clausula) that seemed to be basis of the motet.
Structural harmonic intervals are prime, octave, fourth and fifth. Note that the medieval system has no harmonic system or chords like we have. Composers built upwards, voice by voice, from the tenor, and each part was given an independent melody.
Hundred years later, Leoninus was called by an anonymous, English student the 'optimus organista', i.e. the best composer of organa (pluralis of organum). This Anonymous IV left a treatise on theory and who mentions Leoninus as the composer of the Magnus Liber, the 'great book' of organum. According to Anonymous IV, Leoninus' work was at the end of the 12th century improved and expanded by the later composer Perotinus.
Perotinus Magnus developed a new genre, so called 'discant organum', in which the voices move more uniformly and the rhythm is more tightly organised by some rhythmical patterns.