In 1954, at the age of 16, he came second in the open backstroke, and after becoming the national junior champion that year, he decided to concentrate on the given stroke.

At the same time, Theile completed his secondary education and was awarded an academic scholarship to study medicine at the University of Queensland.

He joined the Australian team at the 12-week winter camp in Townsville, where he worked under the tutelage of Forbes Carlile.

After some officials had questioned his turning style during the heats, Theile refused to give a demonstration to the judges as his team manager had previously promised them.

[1][3] Subsequent to the Olympic Games were the 1957 Queensland Championships, where Theile was disqualified for the only time in his career, after officials ruled that he had performed an illegal turn.

In 1958, Monckton took the 110 yd backstroke world record as National Service prevented Theile from competing.

He subsequently returned to medical studies for the rest of the year, when he moved to Warwick, Queensland, south of Brisbane to resume training with Cusack.

[1] Theile arrived in Rome as an outsider, despite being the defending champion as he had not regained his form of four years prior, with Robert Bennett and Frank McKinney of the United States posting faster times.

Theile attacked at the outset in the final, as was his style, and held a slender lead at the 50-metre mark over McKinney and Bennett.

Theile made a good turn, lengthening his lead to half a body length, before holding off a late surge to claim consecutive gold medals, defeating McKinney by just 0.2 s, setting a new Olympic record in the event.

[4] For the first time, the 4×100-metre medley relay was contested at the Olympics, and combining with Terry Gathercole, Neville Hayes and Geoff Shipton, the Australians finished well behind the Americans to win the silver medal.

After obtaining further experience in the United Kingdom, in 1974 he entered private practice as a general surgeon in Brisbane, and was appointed to the visiting staff of the Princess Alexandra Hospital.

In 2001, Theile was awarded the highest honour from the Royal Australasian College of Surgeons, the Sir Hugh Devine Medal.