One Crime, Two Codes: How the BNS-BNSS-BSA Transition Shaped India's Constitutional Docket in 2025

As Supreme Court year-end reviews tally 2025's landmark constitutional judgments, one recurring thread runs beneath them: courts nationwide are now navigating two parallel criminal codes at once, and the seams are where the constitutional questions live.

Through 2025, the first full year after India's criminal codes were overhauled, courts had to try cases under two parallel systems: offences committed before 1 July 2024 continue under the IPC and CrPC, while later offences fall under the new BNS and BNSS. This meant the same court could handle near-identical cases under entirely different section numbers and, at times, different procedures.

The scheme rests on the savings clauses—BNS Section 358 and BNSS Section 531—which preserve old-law proceedings rather than repealing them outright, giving statutory effect to Article 20(1)'s bar on ex post facto criminal liability. Courts, however, have leaned towards applying beneficial procedural upgrades under BNSS (such as Section 479's undertrial detention cap, or safeguards on arrest and recording) even to pending old-law trials, since procedural law generally applies to pending proceedings unless it prejudices the accused, complementing Article 21's fair-trial guarantee.

Aspirants should remember: substantive law (BNS) is prospective only, protected by Article 20(1); procedural law (BNSS) can apply to pending cases if beneficial; and savings clauses (BNS S.358, BNSS S.531, S.4) manage this transition—key for questions on the IPC-BNS mapping and constitutional limits on retrospective criminal law.