Is the sentence below correct?
I'd like to become a known entity with decision makers in our organization.
On first reading, that sounds like an intentionally humorous misuse of the normal meaning of known entity.
Normally, a Known Entity is an object whose values are fully understood, one which will behave in a completely predictable fashion and which therefore will cause no surprises.
Becoming known to decision-makers in the organization means that you want to increase your visibility within your company, make people aware of you, and presumably pave the way to improve your position.
Based on the normal meaning, becoming a known entity to decision-makers carries the implication that they will never need to consult with you because they'll always know what you would say.
(also, as FX_ says, "to" is a better preposition to use.)
I think it is correct if you replace with with to: “a known entity to decision makers”.