Yes, when executed properly, a Non-Disclosure Agreement is legally binding. The parties to the contract are held to Singapore’s Law of Contract.
A valid contract must include some consideration, which means each party receives some benefit from the agreement. So, for example, it may be difficult to enforce a new NDA against an existing employee if they don’t get a raise or a perk in exchange for the newly created obligations.
Also, an NDA will not be enforceable if the confidential information becomes publicly known (through no fault of the receiving party) because it can no longer be defined as confidential information.
For instance, imagine two inventors entering into an NDA with a potential investor. The investor agrees to keep the details of the invention confidential until they can begin manufacturing and selling the new product.
If one of the inventors gives away the secrets of the invention during an interview with a journalist, the information would be considered public knowledge, and the investor could not be held accountable by the inventors if that information is used by third parties.