Duminy is a successful batsman generally occupying the top order, a skilled fielder and a useful change bowler. He became known during the South African under-19s tour to England in 2003 and in the 2003-04 domestic season, where he averaged over 72, two years after breaking into South Africa's Western Province side. Though he bowls less frequently in One Day Internationals, he has also found success with the ball, making his ODI debut in 2004 against Sri Lanka.
Replacing injured vice-captain Ashwell Prince, Duminy made his Test debut against Australia at the WACA in Perth on 17 December 2008, scoring 50 not out in the second innings by hitting the winning runs in the match after putting on an unbroken century partnership with AB de Villiers. His performance was lauded by numerous critics, including Peter Roebuck. In the next Test match, beginning on Boxing Day, Duminy combined with the tailenders to score his maiden Test century of 166. South Africa were more than 200 runs in arrears when they lost their seventh wicket in the first innings. In the process, he and Dale Steyn (76) put on 180 and surpassed Graeme and Peter Pollock's South African ninth wicket partnership record against Australia. South Africa ended with a 62-run lead and converted it into a nine-wicket win. This sealed the series, the first time that South Africa had won a Test series in Australia, and Australia's first home Test series loss in 16 years.
He also took his first test wicket, Michael Clarke during that tour in the 3rd test, and took one of the freakiest catches ever seen in the 2nd Twenty20 international against Australia in Brisbane. David Hussey skied a ball up in the air and Duminy, while running towards the boundary, flung himself in the air, dived, and took the catch with two hands.
Duminy became the second batsman after Adam Gilchrist to be dismissed for 99 in a World Cup match. Overall, there have been 36 occasions when a player has been dismissed in the nineties in World Cups.