The centenary year of Lokamanya Tilak's demise is being observed during 2020-2021. We know him as a statesman, journalist, leader of the masses, educationist, man of Mathematics, Astronomy, etc. But he is hardly considered as a philosopher. He has produced a purely philosophical treatise and has interpreted Bhagavad-Gita as Niskama Karma -Yoga-Sastra. Gita as Karma-Yoga-Sastra is hardly known to the English-speaking world. The thesis is the first attempt to present the Gita-Rahasya as purely philosophical in spirit. Its duty-centric message has universal appeal across nations and continents, age and gender. Primarily, Gita-Rahasya spells out Hindu view on life, religion and morality. It is argumentative, logical, rational, analytic and is neither narrow nor dogmatic. Like Bhagavad-Gita, the spirit of synthesis discerned in the Gita-Rahasya is highlighted in the thesis which assimilates all odds and transcends all pairs of opposites-Tradition and Modernity, Faith and Reason, Altruism and Egoism, Spirituality and Materialism, Religion and Science. The thesis systematically proceeds elaborating Metaphysics described in the Gita, discussing various ethical issues centered around Arjuna's dilemma and the vision it imparts. The tenets are examined critically in the light of Applied Ethics, Meta-ethics, Hermeneutics, Post-Modernism and Comparative Philosophy. With critical appraisal, the thesis introduces Gita-Rahasya, a Marathi text in simple English and highlights its significance in facing challenging situations in the present times. Contents - Introduction Chapter I - Gita-Rahasya as Transcendent Metaphysics Chapter II - Gita-Rahasya as Normative Ethics Chapter III - Gita-Rahasya as Contemporary Ethics Chapter IV - On Exploring Further Possibilities References and Endnotes Bibliography Synopsis (Appendix A) Pure Reason ani Shuddha Buddhi (Appendix B)