Prosser was born in Melbourne, Victoria, and first competed for Australia at the 2006 Oceania Swimming Championships in Cairns where he won gold medals in the 50 and 100 metre freestyle events and with Kirk Palmer, Tim La Forest and Grant Brits won gold in the 4 × 100 metre freestyle relay, setting a new championship record in each event.

His breakthrough was at the 2010 Australian Swimming Championships in Sydney where Prosser won the silver in the 50 metre freestyle behind Ashley Callus.

[5] (Note: due to the fact that Prosser finished behind three other Australians, Kyle Richardson, Eamon Sullivan, and James Magnussen he was ineligible to contest the B final.)

However, when Prosser teamed up with Richardson, Sullivan, and Magnussen they won silver in the 4 × 100 metre freestyle relay, finishing behind the United States.

[8] Sullivan replaced Prosser and the team went on to win in the final in a Games record time of 3:13.92.