Experiments that excluded pollinators from flowers have shown Jesup’s milk-vetch to be capable of self-fertilization. However, bumblebees identified as Bombus vagans vagans, a widespread and common species, have also been observed visiting Jesup's milk-vetch flowers. 

Jesup’s milk-vetch plants emerge in April, or as soon as ice cover and temperature permits, and bloom in early to mid-May. Flowering generally lasts to early July, and seed set occurs from late June to mid-July as W. Brumback noted in 2009. Most fruits have dehisced, or have released their seeds, by early July. Some fruiting stems typically wither by mid-August, but M. Brumback and M. Piantedosi noted in 2018 that the vegetative stems of the plants usually remain green until September or October. W. Brumback also noted in 2009, that seed germination doesn't occur until the following year or later.

Recent life history investigations by C. Kane tracked individual plants at all three populations, documented low numbers of plants surviving up to three years and indicated that the typical lifespan of the Jesup’s milk-vetch is generally three years. Additionally, C. Kane's observations during the growing season documented that there is some die-off of older plants throughout the season while new plants continue to emerge into August. 

Jesup’s milk-vetch is distinguished from its closest known relative, Astragalus robbinsii var. minor - the only variety with which it could potentially co-occur, on the basis of range - by its “nearly glabrous foliage and especially by the elongate, erect or gently declined cusp terminating the distinctly but very gently decurved pod,” as described by R.C. Barneby in 1964.

The Jesup's milk-vetch has small purple, pea-like flowers, tiny leaflets that make up the compound leaves, a deep tap root and flattened seed pods with seven or more seeds.

Jesup’s milk-vetch plants are found in the Connecticut River valley in central New Hampshire and Vermont along the main stem of the Connecticut River. The plants live in crevices on ledges or shelves of bedrock outcrops where little soil has accumulated and there is not much shade. The habitat needs to be annually scoured by ice or spring floods to replenish the soil and remove other plant species, particularly invasive, non-native plants that will otherwise take over Jesup's milk-vetch habitat. The stretch of the Connecticut River where Jesup's milk-vetch is found also provides habitat for several other state and federally listed species, including the dwarf wedgemussel (Alasmidonta heterodon), the cobblestone tiger beetle (Cicindela marginipennis) and numerous state-listed plant species.