Did President George Washington have a british accent? Were British English and American English even different at that time?
It depends on what you mean by an American accent, although it is almost certain that George Washington had an accent of the region of Boston, at that time it was nothing like the stereotypical accent of modern Boston.
It is an interesting phenomenon of colonial dialects that often the accents used in these regions take longer to adapt and change from their original accent and often traditional aspects of the dialect remain long after they have been abandoned in the home nations of the colony. This means that the Boston English of the time would have most definitely been different from the English spoken in London at the time but also that in many ways would have retained many aspects of antiquated English that had been lost in British English.
In short, yes George Washington did have an American accent, but it is likely that his accent retained many antiquated aspects of the English language that had already been changed in British English, which means that in one sense George Washington’s accent was more British than the accents of London at the time.