Under international law, the law and practices pertaining to treaties is governed by the Vienna Convention on the Law of Treaties, 1969. Although India is not a Part to the Convention, it follows its provisions in practice. According to the Indian Constitutional scheme, making of international treaties is an executive act. A Treaty is concluded with the approval of the Union Cabinet. It is not placed before the Parliament for discussion and approval. However, where the performance of treaty obligations entail alteration of the existing domestic law or requires new enactment, it world accordingly require legislative action. 

Treaty making formalities –

• Drafting and Negotiation – The Ministry of External Affairs is overall in-charge of international treaty making activities. The administrative Ministry is the nodal agency for preparation of drafts, consultations and negotiations. 
• Approvals – After the text of the Treaty has been negotiated and finalized, the administrative Ministry processes for necessary approvals of the Minister concerned and thereafter the External Affairs Minister’s approval is obtained. Tee administrative ministry then moves Cabinet note for its approval. 
• Full powers – The person designated for signing the treaty would require Full Powers from the President of India authorizing him to sign.
• Ratification – Where a treaty does not provide for its entry into force upon its signature only, and makes it subject to ratification, the treaty requires ratification. Multilateral Treaties are, however, always subject to ratification. The treaty is ratified by obtaining the Instrument of Ratification under the signature and seal of the President of India. 
• Accession – Accession is the procedure for becoming a part of a treaty where a country has not signed the treaty during the period it was open for signature. In such a situation, a country accedes to the treaty without having signed it.

Source: MEA