Nine-leaf desert parsley is a perennial wildflower with one to a few erect stems arising from 20-80 cm high from a narrow, elongate taproot. The herbage is covered with fine, short hairs. The leaves are mostly basal, although some may be present at the middle or upper parts of the stems. The leaves are ternately or ternate-pinnately compound 2-3 times, and cleft into long, narrow segments or leaflets from 1-10 cm long.

The inflorescence is an umbel with 6-18 stems of unequal length supporting the umbelets, these stems measuring up to 3-6 cm long. The flowers are yellow. The fruits are oblong to broadly elliptic with narrow to broad wings, and measuring from 7-15 mm long. The bracts below the umbelets are filiform or are absent.

Nine-leaf desert parsley could be confused with slender-fruited desert parsley (L. leptocarpum). The latter species has roots that have elongated or beaded swellings while the former has thick roots which lack the swellings. The latter species is also often 4 times pinnately compound with shorter leaf segments, while the nine-leaf desert parsley is tri-pinnately compound with longer, leaf segments (with the exception of L. triternatum var. anomalum, which has shorter, borader segments).

Nine-leaf desert parsley may be found on open slopes and in dry to fairly moist soil in meadows from the lowlands to moderate elevations in the mountains.

Nine-leaf desert parsley may be found from southern British Columbia south through Washington and Oregon on both sides of the Cascade Mts. to California and east to southern Alberta, Montana, Colorado and Utah.