Theron made his debut for Eastern Province in October 2005, appearing in a List A match at Port Elizabeth against the Zimbabwe U-23 team, bowling them out for 145 and thus helping his team win the fixture with match figures of 2/26 of 6.3 overs. He soon made his first class debut in November 2005, appearing against KwaZulu Natal. He soon showed his potential and developed into an important member of the Warriors side, leading the team in subsequent bowling charts in both first-class and List A competitions.
In 2008, Theron's performances for Warriors led to him being awarded the MTN Domestic Championship Cricketer of the Year award in Cricket South Africa's 2008 Mutual Federal SA Cricket Awards. Also during the same year, he played English club cricket for Staffordshire-based club Audley, where he replaced fellow South African Alfonso Thomas. He also represented the South Africa A side during the same year.
Theron's strong domestic performances in all competitions, notably during the Standard Bank Pro20 series, led to him being awarded both a place in South Africa's 18-man provisional 2010 ICC World Twenty20 squad, a national contract and signing with Indian Premier League team Kings XI Punjab. In his debut for Punjab against the Chennai Super Kings, he recorded impressive figures of 2/17 in his four overs and bowled the Super Over that led his team to an unlikely victory, subsequently being awarded with the Man of the Match award. He played in the two T20 Internationals against Zimbabwe and during the ODI series he took his first ODI wicket that of opener Hamilton Masakadza. He bagged 11 wickets in the three-match ODI series against Zimbabwe including a five-wicket haul.
He was then selected for the two match twenty-20 series against Pakistan but not the ODI series. He bagged 4 wickets in the two match series and was subsequently the selectors decided to add Theron for the ODI series against Pakistan  Theron was picked up by Deccan Chargers for IPL for the season of 2011.
Theron (31 off 16) and Wayne Parnell (29 off 11) produced a stunning partnership as South Africa won the second T20I against Australia despite looking dead and buried at 84/7.