Graham Johnston had the following podium finishes at major championships: 1st in the 1950 British Empire Games 1650 yards Freestyle, 1st in the 1954 British Empire and Commonwealth Games 1650 yards Freestyle, 2nd in the 1950 British Empire Games 440 yards Freestyle, 3rd in the 1954 British Empire and Commonwealth Games 440 yards Freestyle, 3rd in the 1954 British Empire and Commonwealth Games 4×220 yards Freestyle Relay (with Dennis Ford, Peter Duncan, and Billy Steuart).
|1952 Summer||22||Helsinki||Swimming||Men's 400 metres Freestyle||South Africa||RSA||5 h1 r2/3|
|1952 Summer||22||Helsinki||Swimming||Men's 1,500 metres Freestyle||South Africa||RSA||5 h1 r1/2|
|1952 Summer||22||Helsinki||Swimming||Men's 4 × 200 metres Freestyle Relay||South Africa||RSA||7|
|1952 Summer||22||Helsinki||Swimming||South Africa||Semi-Finals||Heat One||5||4:45.5|
|1952 Summer||22||Helsinki||Swimming||South Africa||Round One||Heat Four||2||QU||4:52.3|
|1952 Summer||22||Helsinki||Swimming||South Africa||Round One||Heat One||5||19:27.1|