A szlachcic, of Jastrzębiec coat of arms, Mikołaj Abramowicz was the son of Smolensk voivode Jan Abramowicz. His birth documents have not survived, but it is recorded that he served as the senior cannon officer (artillery leader) during the 1621–22 war with Sweden. In subsequent conflicts with Sweden, he fought in the failed 1625 campaign, capturing the bridge crossing at Daugava, and particularly distinguished himself as a regimental commander during the 1626–29 war, in the Battle of Vistula.