I was wondering if it was grammatically correct to use the word "fired" in a context similar to : "We fired the client as he had become annoying over time"

I though that "fired" could only be used in the context of an employer "firing" an employee not an employee "firing" an employer.
Hi, plebz. Thanks for joining us. Welcome to English Forums.

I'd call your usage of "to fire the client" creative, if not poetic. I doubt you'll find it in a standard dictionary, although it may appear in a business dictionary. I have heard the expression used a couple of times. If it gains in popularity over time, it will probably find its way into the standard dictionaries.

It's also possible that what's being misused here is the term "client." There are some business arrangements where subcontractors are referred to as "clients," for legal purposes, although in a practical sense they're considered employees, and may be fired (have their contracts terminated.) "Client" is more traditionally used to refer to a customer.

Best regards, - A.
Thank you for the reply, much appreciated.