Pigeonpea (Cajanus cajan (L.) Millspaugh; Fabaceae) is an important food legume crop of equatorial and semi-arid parts of the world. Our two years consecutive study on a short duration cultivar of pigeonpea (ICPL 15011) grown under enriched CO2 conditions (open top chambers; 550μmolmol-1) showed significantly high net photosynthetic rates (A’) and foliar carbohydrate content (36% and 43% respectively) which further manifested in dry biomass at harvest, with an increment of 29% over the ambient plants. Also, in vivo carboxylation efficiency was increased by 24.6% suggesting the absence of Rubisco limitation. Chlorophyll a fluorescence measurements, as indicated by Fv/Fm and Fv’/Fm’ ratios, justified enhanced photosystem II efficiency. Mass and number of nodules exhibited prodigious accretion in elevated CO2 grown plants showing 58% increase in nodule mass ratio (NMR) which directly correlated with A’. Stem and root anatomy showed an increase in the number and diameter of xylem vessels in high CO2 grown plants. An increased phloem cross sectional area in high CO2 grown pigeonpea suggested better mobility of sugars from leaf to root and subsequently to a greater sink capacity in the form of root nodules. Ultrastructure of nodule revealed the distribution of bacterial colonies in the infected zone of nodule. Further, growth under high CO2 extended life cycle of Pigeonpea with delayed flowering and pod setting by nine days. The results demonstrated a developmental reprogramming in pigeonpea due to lack of photosynthetic acclimation and increased carbohydrate - nitrogen reserves which were associated with varied vegetative and reproductive growth patterns under elevated CO2. Our study clearly suggest that the predicted future elevated CO2 atmosphere favour pigeonpea to sequester more atmospheric CO2 and N2 resulting better economic yields under natural habitats.