I think the first president would've been George Washington.
Is this a complete sentence or it needs further context to be complete?
It's a complete sentence. Broadly speaking, context is not required to make a sentence complete. It is required to make the meaning understandable.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
It's a complete sentence.
Broadly speaking, context is not required to make a sentence complete. It is required to make the meaning understandable. eg He did it is a complete sentence, but we don't know who did what..
would've been is not the natural choice of verb here.