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.