Gamma irradiation induces various physiological, biochemical alterations in plants with modulation of certain metabolic and defensive pathway. Pre-sowing seed irradiation is considered as an effective method of improving production, yield components and chemical composition in plants. In the present study Cajanus Cajan was subjected to gamma irradiation with absorbed doses 0 Gy, 30 Gy, 50 Gy, 100 Gy, 150 Gy and 200 Gy with a dose rate 2.08 Kilo Gray per hour (2.08 KGh-1). Cajanus cajan when exposed to variable doses of gamma radiation showed persistent changes in the growth and development under both in vivo & in vitro conditions. Radiation sensitivity test based on germination percentage of irradiated and non-irradiated seeds demonstrated that significant reduction in germination percentage was observed with increasing gamma dosage under both in vivo and in vitro conditions. Biochemical analysis confirmed that protein, photosynthetic pigments, proline are very sensitive to gamma radiation, and are good indicators of tolerance. Effective stimulatory dose for plant development under in vivo conditions is 100 Gy while the absorbed doses of 150 Gy and 200 Gy can prove detrimental. However under in vitro conditions, results hold 150 Gy as threshold dose for increasing plant growth, plant vigour and development. Conclusively productivity of Cajanus cajan and consequent economic gains could be enhanced through adoption of suitable cultivar and level of gamma radiation. Gamma rays prove to be an important tool in increasing the breeding efficiency and regeneration frequency, especially that of the recalcitrant varieties. Results in the present study provide sufficient evidence to the effect that γ-irradiation does activate a biochemical system.