As polemarch, Callimachus had a vote in military affairs along with the 10 strategoi, the generals, such as Miltiades. Miltiades convinced Callimachus to vote in favour of a battle when the strategoi were split evenly on the matter.
At Marathon, Callimachus commanded the right wing of the Athenian army. The right and left wings (the left wing commanded by the Plataeans) surrounded the Persians after a seemingly suicidal charge by the centre line. Although the Greeks were victorious, Callimachus was killed during the fighting.