As you probably know, a cause of action against a lawyer for "breach of fiduciary duty" is different than a cause of action for malpractice. The latter is clearly a cause of action in tort which requires the plaintiff to meet the elements of a negligence claim. The former, however, is different and, in fact, sometimes allows a plaintiff to state a claim under circumstances where a claim for malpractice will not be recognized. See Tante v. Herring 453 S.E.2d 686 (Ga. 1994) for an example of this.
Having said this, then is a cause of action for breach of fiduciary duty not a torts claim? If not, what type of claim is it? A claim for breach of contract, perhaps? I imagine there are cases out there that have addressed this question, but I have not done the research to determine what seems to be the majority view on this.
What I can tell you today is that there is a new case on the subject and that it holds the claim is a torts claim. Interestingly, the holding worked in favor of the defendant because the statute of limitations just happened to be shorter for torts claims.
As reported in the Legal Profession Blog, the Connecticut Supreme Court concluded that "the plaintiff’s allegations sound in tort rather than in breach of contract, and, as a consequence, the plaintiff’s claim is barred by the three year statute of limitations applicable to tort claims."
The case is called Meyers v. Livingston and you care read it here.