What is the difference between legal and lawful?

Answer 1

The only real difference between legal and lawful is that what is considered lawful may not be legal.

Another Perspective

A lawful act contemplates the substance of law. It is authorized, permitted, sanctioned or not forbidden by law.

A legal act is performed in accordance with the forms of law or in a technical manner. In that sense, illegal is regarded as invalid.

A common example would be a Last Will and Testament that does not conform to the rules in the jurisdiction. It might be regarded as invalid or illegal but not unlawful since writing an invalid Will does not violate any law. It simply is invalid because it does not conform to the technicalities of law and will not be approved by the probate court.