In April 2016, McCartney was selected to compete at the 2016 Summer Olympics in Rio de Janeiro. In the Olympic final, she cleared 4.50 m, 4.60 m, 4.70 m, and her personal best 4.80 m on her first attempts, but was eliminated after failing to clear 4.85 m. Her 4.80 m result and no misses up to that height saw her place ahead of Australia's Alana Boyd to win the bronze medal. At age 19 years and 252 days, McCartney became the youngest Olympic medallist in the women's pole vault. She was also only the fourth New Zealand Olympic medallist in a field event, after Yvette Williams (long jump, 1952), Valerie Adams (shot put, 2008, 2012, 2016), and Tomas Walsh (shot put, 2016). BMX rider Sarah Walker, an Olympic silver medallist, approached McCartney at the Halberg Awards ceremony on 18 February 2016 and has been mentoring her since.