Dominic John Grehan Mahony MBE (born 26 April 1964) is a British former modern pentathlete. He competed in the 1988 Summer Olympics and at the 1992 Summer Olympics, winning a bronze medal at the 1988 Games. In 1986, he won the épée title at the British Fencing Championships.
Mahony attended Millfield School from 1977 to 1982. He was appointed Member of the Order of the British Empire (MBE) in the 2014 New Year Honours for voluntary services to modern pentathlon.