[2][3] He served as military governor (strategos) of the Armeniac and Bucellarian themes in Asia Minor, before being sent to Thessalonica as doux in c. 995, in succession to Gregory Taronites, who had been killed in a Bulgarian ambush.
[6] He was certainly at his post as governor of Thessalonica in September 995, for he issued an act (sigillion) confirming various privileges and exemptions of the Kolobou Monastery at Ierissos on Chalcidice, which survives to this day.
[6][7] Following the death of Taronites and the capture of Chaldos, Basil II appointed one of his most trusted subordinates, Nikephoros Ouranos, as commander-in-chief in the Balkans, resulting in the crushing victory over Samuel and his army at the Battle of Spercheios.
[8][9] John Chaldos is mentioned next, and for the last time, during the 1030 campaign by Emperor Romanos III Argyros against the Mirdasids of Aleppo, which he advised against.
The Emperor did not heed his opinion, and the campaign ended in a humiliating defeat in the Battle of Azaz.