Was the adhirat charioteer of bhishma in mahabharat?

No, Adhirath was not the charioteer of Bhishma in the Mahabharata. Adhirath was the charioteer of Karna, one of the key warriors in the epic. Bhishma's charioteer was actually a character named Sarathi, who drove Bhishma's chariot during the Kurukshetra War.