The obvious reason is that the verb “hear” and the adverb “here” are pronounced the same. Hear, hear is often confused with here, here. Hear, hear can also be used as a cheer that’s why you sometimes hear it at the end of toasts.
So you can replace hear, hear with phrases such as “I agree wholeheartedly,” “what he/she said,” or “yeah,” depending on the formality of the setting and the speakers. When you say hear, hear, you are in fact saying that you agree with something another person has just said. Sometime during the eighteenth century hear him, hear him acquired its short form, hear, hear, and that form is still used today. And in case you were wondering, there was no “hear her, hear her” variation-the first female MP was elected in the twentieth century.
The UK Parliament prides itself on its lively debates, and saying “hear him, hear him” was a way to draw attention to what a person was saying. The phrase hear, hear seems to have come into existence as an abbreviation of the phrase hear him, hear him, which was well-established in Parliament in the late seventeenth century. Origin and Meaning of the Phrase Hear, Hear
