Laches is a legal doctrine that bars those who take too long to assert a legal right to any entitlement to compensation or relief.
In order to establish the defense of laches, a party must show undue or unreasonable delay by the other party in asserting its rights, and prejudice resulting from the delay.
A trademark owner can’t wait 10 or 20 years before filing a trademark infringement action in Canada, based on the doctrine of laches. However, laches is not an available defense to a fraud claim.
In Scott Technologies Inc. v. 783825 Alberta Ltd., 2015 FC 1336, Justice Zinn concluded his reasons with a comment on the inaction on the part of the plaintiff in regards to the defendant’s use of the Scott Safety name:
 … Here, the plaintiff has long known of the use by the defendants of “Scott Safety” … but it did nothing … until it decided to globally rebrand itself as Scott Safety – the defendants’ very trade-mark. A business cannot lie in the weeds, allowing another to carry on and invest in and grow its business, and then spring up and enlist the aid of the court when it suits its purposes, claiming it has been unfairly treated. In this case, if there is any unfairness, it is that the defendants were unfairly treated by the plaintiff when it decided to use the same name the defendants had been using in excess of 20 years.
A legal doctrine whereby those who take too long to assert a legal right, lose their entitlement to compensation.
When you claim that a person’s legal suit against you is not valid because of this, you would call it estoppel by laches.
The pivotal case on the doctrine of laches is an 1874 British case, Lindsay Petroleum Co. in which the Court stated:
“(T)he doctrine of laches in Courts of Equity is not an arbitrary or a technical doctrine. Where it would be practically unjust to give a remedy, either because the party has, by his conduct, done that which might fairly be regarded as equivalent to a waiver of it, or where by his conduct and neglect he has, though perhaps not waiving that remedy, yet put the other party in a situation in which it would not be reasonable to place him if the remedy were afterwards to be asserted, in either of these cases, lapse of time and delay are most material.
“But in every case, if an argument against relief, which otherwise would be just, is founded upon mere delay, that delay of course not amounting to a bar by any statute of limitations, the validity of that defence must be tried upon principles substantially equitable.
“Two circumstances, always important in such cases, are, the length of the delay and the nature of the acts done during the interval, which might affect either party and cause a balance of justice or injustice in taking the one course or the other, so far as relates to the remedy.”
This was quoted with approval in Canada’s Supreme Court in MK v MH.
In a more recent Ontario case, Cosentino v Roiatti, the Ontario Superior Court of Justice used these words:
“(A) defendant can successfully resist an equitable claim made against him if he can demonstrate that the plaintiff, by delaying the institution or prosecution of his case, has either acquiesced in the defendant’s conduct, caused the defendant to alter his position in reasonable reliance of the plaintiff’s acceptance of the status quo, or otherwise permitted a situation to arise which would be unjust to disturb.”
“Ultimately, laches must be resolved as a matter of justice between the parties, as is the case with any equitable doctrine.”