Born in London, England, Teddy Flack was five years old when his family migrated to Australia. Soon after leaving the Melbourne Church of England Grammar School in 1892, where he studied Greek history, Flack became the one mile champion of New South Wales and Victoria. After graduation Edwin joined his father's accountancy firm, Davey, Flack & Co. At the age of 21 Flack was sent to London to receive further training as an accountant with the firm Price Waterhouse. A keen athlete in Australia, Flack joined the London Athletic club and was intent on attending the coming inaugural Olympics while in Europe.
He reached Athens after an uncomfortable six day rail and sea trip, during which he was plagued with sea sickness. On the opening day of the Games he won his first race, the first heat of the 800 m run. On the second day he lined up against the American favourite, Arthur Blake, in the 1500 m run. Running shoulder to shoulder with Blake in the final straight, Flack powered ahead near the end to win by more than five metres. On the fourth day of the Games Flack earned his second first-place medal, winning the 800 m run.
Just a day later Flack tried for a treble, in the marathon, even though he had never run a race more than 10 miles, less than half the marathon distance. He was in second place behind Frenchman Albin Lermusiaux, bronze medallist in the 1500 m run, for much of the race. After 32 kilometres, the Frenchman dropped out and Flack was left in the lead. But with just 4 kilometres to go, Flack suddenly collapsed. He was so delirious that, when a Greek spectator tried to help him, Flack punched him to the ground. He was disqualified and ostracised by the other athletes.
What is little known is that Flack also competed in the tennis singles and doubles at the Athens Olympics. He lost in the first round of the singles. In the doubles he was paired with an English friend, George Robertson. They reached the semi-finals after a walk-over in the first round, but lost their only match. They placed third due to their semi-final appearance, but medals for third places were not yet awarded in 1896.
He returned to Australia and the family firm in 1898 and lived on a property near Berwick, in Victoria, where he bred Frisian cattle. Flack never competed for Australia again. Instead he attended to his accountancy business.