[2] Together with his brother Paul he won the gold medal in the lightweight double sculls at the 2016 European Rowing Championships, silver in the same discipline at the 2016 Summer Olympics,[3][4] and gold at the 2018 World Rowing Championships.

[12] In April 2016, Paul and Gary O'Donovan won silver in the lightweight double sculls at the first World Rowing Cup events of the year in Varese, Italy.

[13] In the following month, the pair won the 2016 European Rowing Championships gold medal in the double sculls in Brandenburg, Germany.

[15] In 2017, the brothers won silver in men's lightweight double sculls at the European Rowing Championships in May 2017.

They also won silver at the second World Rowing Cup regatta of the season in Poland in June,[16] and bronze at the third in July.