At the 2012 Olympics in London, Boyle was fourth fastest in the heats of the 400m freestyle in a New Zealand record 4:03.63. In the final she finished 8th. In the 800m heats she swam 8:25.91, also a New Zealand record, qualifying fifth fastest for the final. In the final she swam another record of 8:22.72 to finish fourth, 2.40 seconds from the bronze medal which went to defending champion and world record holder Rebecca Adlington.
At the 2014 Commonwealth Games, Boyle won gold in the 400m freestyle and a silver medal in the 800m freestyle. She also finished fourth in the final of the 200m freestyle after breaking the New Zealand record in the heats.[3] In the 400 m freestyle, she set a new Games record in the final.[4]
At the 2016 Summer Olympics, Boyle was 14th fastest in the semi-finals of the 400 m freestyle, and did not make the final.[6] In the 800 m freestyle, she was 0.29 of a second off making the final.
Boyle is a graduate of the University of California, Berkeley. She announced her retirement from competitive swimming on 1 August 2017 due to ongoing injury problems.