What is the origin of the expression speak truth unto power?

Answer 1

The phrase "Speak Truth to Power" comes from a 1950's American Friends Service Committee (Quaker) pamphlet.

source:

Please see the related link below.

Assuming that site is correct, unless Professor Hennessy was quite precocious, he didn't originate the phrase, though he may have helped popularize it and may have added the "unto".

The phrase "to speak truth unto power" has long been associated with the British Civil Service. To be able to "speak truth unto power" (i.e. give honest and objective advice to ministers) has always been seen as something that all impartial civil servants should be able to do.

The phrase is particularly associated with the eminent historian and academic Professor Peter Hennessy of Queen Mary College London. It is a phrase he has used on many occasions during his distinguished career as a "Whitehall Watcher".