Legal Definition of Attorney-in-fact:  An individual who is authorized by a written document to act for another. The individual need not be an attorney and the written document is often called a Power of Attorney | Discover the Power of Attorney-in-Fact: What it Means and Why You May Need One – As a business owner, understanding the definition and benefits of an attorney-in-fact is crucial. Learn how this authorized individual can make decisions on your behalf when you’re unable to. Find out more here.