This term for an important person dates to the 18th century. It’s a reference to the powdered wigs that men wore back then. Rich and important men would have larger, more expensive wigs, hence the term.
Slang etymologist Eric Partridge dates the term to 1731, but provides no citation or context for the usage. This, like many of Partridge’s dates, is suspect. The earliest citation in the Oxford English Dictionary is from a 1781 letter by English politician George Selwyn, who is notable for having served 44 years in the House of Commons without ever once making a speech:
A new point of discussion for the lawyers, for our big wigs, for their Lordships.
Contrary to the bit of internet folklore that is floating about, men did not shave their heads under the wigs (or at least most didn’t) and the wigs were not placed in a loaf of bread and baked in order to clean them. That is simply absurd.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton