Making his international debut at the 1964 Tokyo Olympics, Reynolds reached the final of the 200-metre backstroke, where he finished last to American Jed Graef, who won in a world record time.

He combined with Ian O'Brien, Kevin Berry and David Dickson to claim bronze in the 4×100-metre medley relay, behind the United States and German.

He collected gold in the 110-yard and 220-yard backstroke and the 400-yard individual medley, beating Canadian Ralph Hutton, setting world records in the latter two events.

Another gold in the 4×110-yard medley relay was lost after Reynolds, O'Brien, Wenden and Graham Dunn were disqualified after a careless early changeover; they had touched the wall far in front of the rest of the field.

Although he increased his tally of Australian Championships to 14 the following year, he failed to gain selection for the 1968 Summer Olympics in Mexico City.