Annals of the Privilege
The legal systems of the U.S. and Canada are roughly rooted in English law and it's after the reign of Queen Elizabeth I that a few incomplete references to attorney-client privilege first show up in the historical record around the 1650s. But the English didn't really get around to battening down the hatches on their jurisprudence until the 1700s. In the period the mid-1600s to around 1743, there are just 14 reported decisions on attorney-client privilege [source: Hazard].
In 1743, the case of Annesley v. Anglesea became a pivotal trial in the history of attorney-client privilege. The story was straight out of Dickens, replete with a scheming uncle and a disinherited nephew. When Arthur, Baron of Altham died, his brother, Richard, Earl of Anglesea was due to inherit the estate as long as his deceased sibling had died childless.
But then an inconvenient chap named James Annesley popped up saying that he was Baron Arthur's long-lost son and rightful heir. According to Annesley's story, he'd been born to Baron Arthur's wife but was kicked out of the house by a jealous stepmother.
Completely broke, Annesley was forced to make his own way before being kidnapped and sold into indentured servitude in a far-flung colony for 13 years. To add to his miseries, he was prosecuted for murder. Luckily for Annesley, he was found not guilty and with the help of former nurses and servants, he was able to re-establish his identity and claim his rightful inheritance [source: Hazard].
In the inheritance case, Annesley alleged that his uncle, the Earl of Anglesea not only knew perfectly well that he had a nephew who was the legal heir to his brother's estate, but that the aforementioned kidnapping, as well as the murder trial, were both his doing. The wicked Earl had apparently gotten his attorney, John Giffard, to trigger the murder prosecution even though he knew that the death in question had been an accident. Giffard had in fact reported, in pre-trial hearings, that the Earl had said of his nephew that he would "give £10,000 to have him hanged."
So, the entire Annesley v. Anglesea case turned upon the question of whether Giffard could give testimony during the trial. The Earl opined that he couldn't, since doing so would violate his attorney-client privilege. Annesley, the nephew, argued, in brief, that the entire business about the murder trial and the notional £10,000 for hanging was not directly related to the case at hand (which, in case you've forgotten, had to do with inheritance) and therefore fell outside the bounds of attorney-client privilege [source: Hazard].
Obviously, attorney-client privilege, while clearly well-established by 1743, was not yet well-defined and that's why Annesley v. Anglesea is considered so pivotal. In the end, the judge agreed with Annesley and ruled that Giffard's testimony did not violate attorney-client privilege. Annesley won the lawsuit, inherited his baronial estate and died a year later, bringing that portion of our story to a happy/unhappy end [source: Hazard].