O'Donovan first won a world championship in the men's lightweight single sculls at the 2016 World Rowing Championships. Together with his brother Gary, he won silver in the Men's lightweight double sculls at the 2016 Summer Olympics, and gold in the same discipline at the 2018 World Rowing Championships. Since 2019, he also partnered with Fintan McCarthy for lightweight double sculls events, and the pair became world champions at the 2019 World Rowing Championships, gold medalists at the 2021 European Rowing Championships, and gold medalists (and world record holders) at the 2020 Tokyo Olympics.