An electrical panel assembly comprising at least one circuit breaker and a mounted low-profile circuit breaker lock-out assembly is disclosed. The circuit breaker lock-out assembly includes a first and second mount. The first mount is for mounting to a first end of a circuit breaker housing wall adjacent a circuit breaker switch lever and includes an outward projection having a through-hole. The second mount is for mounting to a second end of the circuit breaker housing wall and includes a pivotally attached arm that is rotatable between an unlocked and locked position in which the arm is aligned with the outward projection allowing a lock to be inserted through the projection through-hole and a corresponding hole in the arm. The arm is shaped to receive the circuit breaker switch lever and hold the lever immobile when the arm is in the locked position and the lock is inserted.