An turned professional in 2011 and earned a spot on the
Challenge Tour via three stages of
qualifying school. In June 2013, An had his best finish to date on the Challenge Tour, tied for second place at the
Scottish Hydro Challenge. In August 2014, he won his first Challenge Tour event at the
Rolex Trophy, making An the first Korean to win on the Challenge Tour. He finished 2014 in third place in the Challenge Tour Rankings, and moved up to the European Tour. In May 2015, he won the BMW PGA Championship at Wentworth. He was only the second player to win both the
U.S. Amateur and the
British PGA Championship, after
Arnold Palmer. In 2016, An played the
Zurich Classic of New Orleans on an exemption, and lost a playoff at the first hole. In 2016, he earned enough money as a non-member to gain a
PGA Tour card for 2016–17. In December 2019, An played on the International team at the
2019 Presidents Cup at
Royal Melbourne Golf Club in Australia. The U.S. team won 16–14. An went 1–2–2 and lost his Sunday singles match against
Webb Simpson. An has been suspended from the PGA Tour for three months in 2023 (August 31 – December 1) for violating the tour's anti-doping policy. He tested positive for a substance banned by the
World Anti-Doping Agency that was included in an over-the-counter cough medicine in South Korea. ==Amateur wins==