Buck cited dysfunction in Congress and plans to focus on Colorado and family after leaving.
He criticized the current state of Congress as the worst in his nine-year tenure, blaming bickering and inefficiency.
Buck has been a dissenting voice within the GOP, notably voting to oust former Speaker Kevin McCarthy and criticizing the party's alignment with Trump.
House Speaker Mike Johnson expressed surprise at Buck's resignation, indicating lack of prior knowledge.
Buck explained his decision to leave without advance notice, fearing leaks and wanting to control the announcement.
Despite Buck's departure, House Republican majority remains slim, requiring careful strategy in legislative efforts.
With the GOP majority now at 218 seats, leadership faces increased pressure to maintain party unity in votes.