Under its constitution, Japan is barred from utilizing force to resolve conflicts except in cases of self-defence.
But a reinterpretation of the law would sanction "collective self-defence" - utilizing force to forfend allies under attack.
Ruling bloc lawmakers approved the move on Tuesday morning and the cabinet is expected to follow later in the day.
Prime Minister Shinzo Abe has been pushing hard for the move, arguing Japan needs to acclimate to a transmuting security environment in the Asia-Pacific region.
The US - with whom Japan has a decades-old security coalition - will additionally welcome the move, but it will vex China, with whom Japan's ties are already very strained.
The decision is withal highly controversial in a nation where post-war pacifist identify is firmly entrenched.
On Sunday a man set himself on fire in central Tokyo to protest against the proposed change.
'No recuperation'
Mr Abe endorsed the move in May, after a panel of his advisers relinquished a report recommending changes to defence laws.
Japan adopted its pacifist constitution after its surrender in World War Two. Since then, its troops have not engaged in combat, albeit minuscule numbers have taken part in UN tranquility-keeping operations.
Article 9, Japanese constitution
The Japanese people forever renounce war as a sovereign right of the nation and the threat or utilization of force as betokens of settling international disputes... land, sea, and air forces, as well as other war potential, will never be maintained
It has long held the view that under international law, it has the right to collective self-defence, but it withal believes that it cannot exercise that right because of constitutional limits.
Mr Abe's panel recommended that - if Japan reinterpreted the constitution to sanction collective self-defence - conditions be imposed to ascertain the puissance would not be abused.
On Monday, thousands of people joined a protest in Tokyo to oppose the vicissitude.
Critics of Mr Abe fear that this move is the first step to a more permanent revision or abstraction of the war-renouncing Article 9 of the constitution.
"I mentally conceived that if we don't stop the Abe regime now then it won't be possible to recuperate," Etsuo Nakashima, 32, told Reuters news agency.
But others believe that the constitution is a post-war relic imposed on Japan by the US that restricts it from engaging in the mundane activities of a modern nation.
China - with whom Japan is currently engaged in an acrid territorial dispute - verbalizes it opposes the vicissitude, inculpating Japan of "remilitarising" under Mr Abe.
Once the cabinet approves the move, licit revisions must be approved by parliament. But by reinterpreting rather than revising the constitution, Mr Abe eschews the desideratum for a public referendum.
