Sieben was coached by Laurie Lawrence, and made his debut at the young age of 15 at the 1982 Commonwealth Games in Brisbane, where he captured a bronze in the 200-metre butterfly, as well as gold in the medley relay.

[3] By the 1988 Summer Olympics in Seoul, Sieben's ability had waned, and the selectors did not choose him for the 200 m butterfly.

He continued onto the 1992 Summer Olympics in Barcelona, but failed to reach the final of the 100-metre butterfly individual event.

He formed part of Australia's 4x100-metre medley relay team that finished 7th in the final, in a national record time of 3:42.65.

[4] In 2020 Sieben was involved in the construction of the North Queensland Cowboys' Community, Training and High Performance Centre commissioning the pools for Chris Williams and Hutchinson Builders.