In a legal malpractice claim, the client has to show that his or her former lawyer 1) failed “to exercise the ordinary reasonable skill and knowledge commonly possessed by a member of the legal profession", and 2) the client was damaged by the lawyer's malpractice. So at its heart, a claim for legal malpractice is a claim sounding in negligence.
Not every mistake by a lawyer constitutes negligence. For example, pursuing a strategy that backfires is not considered malpractice, so long as the strategy was reasonable.
The Three-Year Statute of Limitations
Under New York law, the suit has to be brought within three years from the time when the defendant-lawyer stopped representing the client. Compared, say, to six-year statute of limitations for breach of contract, the three-year statute of limitations is very short. So a client who has been wronged must keep close watch over the exact date when the lawyer stopped representing him or her.
The Need to Hire an Expert Witness
In order to show that the lawyer failed to exercise reasonable skill and knowledge, the best practice is to have an expert witness give an opinion to that effect. Such witness typically bill at $500/hr. so it's not going to be cheap. A client should count on paying anywhere between $5,000 to $10,000 or more for an expert witness.
The Need to Show Damages or "Loss Causation"
On its face, the need to show damages doesn't sound difficult. But it is: the client has to show that, in the absence of the malpractice, the client would have won the underlying dispute. That is why legal malpractice claims are often called a law suit within a law suit.
Fortunately, the client doesn't have to show to a mathematical certainty that he or she would have won the underlying law suit. All that's called for is a showing by "a preponderance of the evidence" that the client would have won the underlying law suit. That is, there must be more evidence showing that the underlying law suit would have been won than evidence showing the opposite.
To take an example, let's say that the client ran a red light and was hit by another car, causing the client devastating injuries. And let's say that the client's lawyer fails to file the client's personal injury law suit within the three year period.
The case on liability is about as strong as it can be. However, the case on "loss causation"-- i.e., that the lawyer's malpractice caused the client's loss of an award for personal injuries-- is weak. That's because, the accident was the client's own fault, and the client can't show that filing the law suit on time would have resulted in a verdict in his or her favor for the personal injuries.
Claims for Breach of Fiduciary Duty and Fraud
One of the murkiest areas in legal malpractice law is when, if at all the client can also claim a breach of fiduciary duty and fraud. It is desirable to claim breach of fiduciary duty because it permits the client to claim pain and mental suffering from the lawyer's misconduct. But many judges dismiss claims for breach of fiduciary duty and fraud as being duplicative of the claim for legal malpractice.
But there is caselaw that, so long as the breach of fiduciary duty and fraud claims are not based on the same facts as the malpractice claim, they may be brought alongside the malpractice claim.
So lets say that, in addition to making errors in handling the litigation, the lawyer intentionally misinforms the client that the client has no claim and should settle for a modest settlement. And let's say the lawyer does that in order to avoid the trouble of going to trial.
Needless to say, the lawyer's misstatement is an intentional act, not an act of negligence, and is therefore based on different facts than a legal malpractice claim. Nevertheless, under such circumstances, may courts will nonetheless dismiss the breach of fiduciary duty and fraud claims as being duplicative of the legal malpractice claim.