The mission blue butterfly has a wingspan of 2.5 to 3.6 centimeters.

In males, the upper side of the wings is iridescent blue with a black border fringed with white hair-like scales. In females, the upper surface of the wings is dark brown, marked with blue basal areas, with a border similar to the male. In males and females, the underside of the wings is pale grey with two rows of irregular white-ringed black spots. The caterpillars are mostly green and the body is covered with short white hairs. 

Mission blue butterfly caterpillars exclusively feed on lupines, primarily silver lupine (Lupinus albifrons), manycolored lupine (L. varicolor) and summer lupine (L. formosus). Adults feed on a variety of nectar flowers among and near lupine patches.

The mission blue butterfly has one new generation a year. Adults fly during the day from March to early July and reproduce among patches of lupines that serve as the larval host plant. Adults travel usually less than 600 meters but up to 2,500 meters from their lupine host plants. Males fly about or perch on or near the lupines and fly out to encounter passing objects to meet receptive females. Females usually lay their eggs on the tops of lupine leaves, preferring new growth. They may lay their eggs on lupine stems, flowers or seedpods.

Eggs can take seven to 32 days to hatch depending on environmental conditions. About three weeks after the larvae hatch, they go dormant in the leaf litter near their host plants until the following spring, after which they awake and continue feeding. The developing larvae have a mutualistic relationship with native ants that defend the larvae from predation and parasitism in return for honeydew secreted by the larvae. However, this mutualistic relationship with native ants may be disrupted by the presence of non-native Argentine ants resulting in increasing rates of predation and parasitism of larvae. Caterpillars pupate on or near the base of lupine plants for about three weeks before emerging as mature butterflies.

After becoming adult butterflies, males live approximately seven days and females approximately eight days. 

Mission blue butterflies inhabit coastal prairie grasslands which are also inhabited by one of its host lupine species. The mission blue butterfly’s host lupines are dependent on disturbances to the land like rodent burrows, rockslides and fires to establish as seedlings. 

Mission blue butterfly colonies can be found in Marin, San Francisco and San Mateo counties in California. Some areas where the butterfly lives include Fort Baker and Oakwood Valley in Marin County, Twin Peaks in San Francisco County, San Bruno Mountain in San Mateo County and from Milagra Ridge through the San Francisco Peninsula Watershed in San Mateo County.