At the 2008 Short Course World Championships in Manchester, Palmer won 4 medals. Two titles over 200-metre and 400-metre freestyle, one silver medal over 800-metre freestyle and a bronze medal with the 4×200-metre freestyle relay.
At the 2008 Australian Swimming Championships, she won the 800-metre freestyle in a personal best time of 8:24.30, thus qualifying for the 2008 Summer Olympics. Also, by finishing 4th in the 200-metre freestyle, she qualified to swim in the relay at the games.
At the Beijing Olympics, 14 August 2008, Palmer won gold for the 4×200-metre women's relay team, with other members Stephanie Rice, Bronte Barratt and Linda MacKenzie. The Australian team overcame world superpowers USA and China to beat the world record of 7:44:31 by 5.78 seconds. Palmer was the fastest swimmer of her team, giving Australia a 3.14 second advantage.
At the 2010 Commonwealth Games, Palmer won the gold medal in the 200-metre freestyle with a time of 1:57:50.
At the 2012 Summer Olympics, she was part of the Australian 4 × 200 m freestyle team that won silver.[4]