Makes Australian National Swim Team

Cody Simpson can add elite swimmer to his already impressive accomplishments, 'cause the 25-year-old just earned a spot on the Australian swim team ... and will compete against some of the world's fastest in the pool at the Commonwealth Games.

Simpson -- musician, actor, and former teen heartthrob -- competed against his fellow countrymates down under on Wednesday ... finishing 3rd in the 100-meter butterfly at the Australian Championships.

And, no shame in finishing behind the first and second place athletes ... both guys are Olympians.

It's not a total shock that Cody performed as well as he did. In fact, as a teenager, Simpson was a top-level swimmer. However, after his music career took…