In the Second Polish Republic, Adam Koc first was incorporated into the Polish Armed Forces, in December 1919, where he was given command of the 201 Infantry Regiment of Warsaw's Defense, which later became a Volunteer Division (31 July - 3 December 1920). Afterwards, he served in the Ministry of Military Affairs, in different positions. A participant in the May Coup, he was promoted in 1926 to be chief of the Command of VI District of Corps in Lwów, a position he held until 1928.

On 10 August 1914, Koc came to Warsaw from Druskininkai on the order of Walery Sławek, to take command of the local branch of the Union of Active Struggle in the Russian partition.[11] Soon afterwards, the Union of Active Struggle and the Riflemen's Association in Congress Poland united under leadership of Karol Rybasiewicz, formerly commandant of the Polish Rifle Squads. Koc became his deputy, and in August 1914, the new body was named the Polish Military Organisation (POW), led by Piłsudski's emissary, Tadeusz Żuliński.[12] The main target of the new organisation was to create sabotage actions behind the Russian army. Koc was one of the members of the Chief Commandment of POW. In addition, Koc commanded the Warsaw district of the organisation from the beginning of 1915. In February 1915 he was advanced to Podporuchik by Żuliński.[13]