Context Introducing legumes into grass-based forage systems may increase herbage nutritive value while reducing the need for inorganic nitrogen fertilisation. Grass–legume intercrops may also enhance herbage yield stability. Aim We evaluated agronomic and nutritional traits of elephant grass (Cenchrus purpureus Schum.) genotypes grown as monocrops and mixed with butterfly pea (Clitoria ternatea L.). Methods Elephant grass genotypes, two tall (Elephant B and IRI-381) and two dwarf (Mott and Taiwan A-146 2.37), were grown as monocultures or intercropped with butterfly pea in a 2-year trial. Herbage accumulation, yield stability, botanical composition and chemical/bromatological variables were evaluated. Key results Herbage accumulation was highest (P < 0.001) in Elephant B under monocropping (21.9 t/ha.year); however, this treatment revealed the lowest yield stability over harvest times (σi2 5.59). All intercrops were more stable than grass monocrops (mean σi2 0.66 vs 2.55). Higher (P < 0.001) concentrations of herbage crude protein were found in intercrops than monocrops (mean 113 vs 90 g/kg). Intercrop herbage lignin contents (mean 57 g/kg) and protein fraction C (mean 61 g/kg) were higher than those in monocrops. Dwarf Mott had higher (P = 0.001) digestible dry matter concentration than dwarf Taiwan (755 vs 745 g/kg). Conclusions Dwarf Mott genotype has outstanding nutritive value because of its higher leaf:stem ratio. Butterfly pea legume added to elephant grass crop in cut-and-carry systems improves herbage yield stability by reducing seasonal effects. Implications Intercropping butterfly pea in grass-based systems enhances yield stability, allowing herbage harvest with good nutritive value.