O’Hanlon was born on 4 May 1988 in Sydney. He is 183 centimetres (6.00 ft) tall and weighs 78 kilograms (172 lb). He has cerebral palsy due to a prenatal stroke. He attended St Joseph’s College, Hunters Hill. He has five sisters, one of whom, Elsa, rowed for Australia’s national team and won the World University lightweight sculling Championship in Trakai, Lithuania in 2006.

In 2005, New South Wales Paralympic Talent Search Co-ordinator Amy Winters, herself a former Paralympian, recruited him to participate in Paralympic sport. That year, he represented Australia for the first time. In December, he moved to Canberra and started training full-time with Irina Dvoskina at the Australian Institute of Sport (AIS) from 2005 to 2016. Aged 19, his records made him the fastest male cerebral palsy competitor in the world. During his career, he has had to deal with painful shin splits.

In 2005, he competed at the German Nationals and European Championships in the 100 m and 200 m events at his first overseas competition. At the IPC Athletics World Championships in 2006, he competed in the T38 100 m, but did not finish; finished third in the T38 200 m event; and won two gold medals in the 4×100 m relay and 4×400 m relay events. At the Australian Championships, he finished first in the T38 100 m and T38 200 m events in 2006, 2007 and 2008. His 2006 title was his first national one, when he won the T38 100 m event.

He competed in the 2008 Summer Paralympics in Beijing, China. There he won three gold medals in the men’s 100 metres – T38, men’s 200 m – T38 and men’s 4 x 100 metre relay – T35–38 events, for which he received a Medal of the Order of Australia. He won all of these events in World Record times, in the T38 100 m event with a time of 10.96 and in T38 200 m event with a time of 21.98. His time of 10.96 was the first time a male cerebral palsy athlete had a sub 11 second record time.

O’Hanlon was AIS Junior Athlete of the Year in 2008, and was also named Athletics Australia’s 2008 Athlete of the Year – Male AWD. Cleo magazine named him as a finalist in its 2008 Bachelor of the Year contest. In 2011, he was nominated for The Age’s Sport Performer Award in the Performer with a Disability category. In 2011, he received a Sport Achievement Award from the Australian Institute of Sport. O’Hanlon was a finalist for the 2012 Australian Paralympian of the Year. In November 2013, he was named Athletics Australia Male Para-Athlete of the Year. In 2014, he was inducted into the Sydney Olympic Park Athletic Centre Path of Champions.

In 2009 and 2010, he took time off from Paralympic athletics to compete in Australia’s able-bodied domestic athletics season. He has a personal goal of being able to beat able-bodied athletes. One of his early goals was to beat the times of fellow Paralympian athlete Tim Sullivan. He accomplished this, and was on a sprint team with Sullivan that won a Paralympic gold medal in the 4×100 m event in Beijing.

At the 2011 IPC Athletics World Championships, he won gold medals in the 100 m and 200 events, a silver medal in the 400 m event, and a bronze in the 4×100 m relay event. He finished fourth in the men’s long jump event. His two gold medals at the event counted for half the total men’s Australian gold medal count.

As of 2011, he is ranked first in the world. In 2011, he was an Australian Institute of Sport scholarship holder training and based in Canberra.

At the 2012 London Games, he repeated his Beijing success in winning the Men’s 100 m and 200 m T38 events. He was the Australian flag bearer at the closing ceremony of the London games.

At the 2016 Rio Paralympics he won the silver medal in the Men’s 100 m T38 in a time of 10.98. He announced his retirement immediately after the event due to personal reasons.

O’Hanlon moved to Sydney in 2016 and returned to athletics after taking up a part-time position in his family’s architecture business. At the 2017 World Para Athletics Championships in London, he won the Men’s 100m T38 in a time of 11.07s (-1.6). In winning gold, O’Hanlon joined Neil Fuller in becoming Australia’s leading medallist at the World Para-Athletics Championships with 11 medals.