The War Games should be the dab term, since that was his first appearance; however, he wasn't a chancellor in that story.
Talk about it here.
The third Time Lord member of the Second Doctor's tribunal sentenced him — with his peers — to exile on Earth. He was also present for the War Lords' trial, and he watched as the War Lord and his guards were dematerialised. He escorted Zoe and Jamie to say goodbye to the Doctor. (TV: The War Games)