Cummins played junior cricket at Glenbrook Blaxland Cricket Club in the Blue Mountains before playing first-grade cricket for Penrith in 2010. In the preliminary final of the 2010–11 KFC Twenty20 Big Bash against Tasmania Cummins took 4 for 16 and was named man of the match. He finished with Nathan Lyon as the leading wicket-taker in the tournament. In March 2011 he made his first-class debut.

He joined the Sydney Sixers franchise in 2011. In 2012 he signed with the Perth Scorchers, but missed the 2012 season due to injury. He made his debut for the Scorchers when they beat the Adelaide Strikers in Perth on 16 January 2014.

Cummins was selected in Australia's provisional team for the ICC Under-19 World Cup to be held in Queensland in August 2012.

Cummins was bought by the Kolkata Knight Riders of the Indian Premier League for the 2014 season. In February 2017, he was bought by the Delhi Daredevils team for the 2017 Indian Premier League for 4.5 crores. In the 2018 IPL auction, he was bought by the Mumbai Indians for a price of 5.4 crores.. Later he was ruled out of the entire tournament due to an injury

Cummins was granted a Cricket Australia contract in June 2011,^[14] and in October 2011 he played two T20I matches for Australia against South Africa. On the basis of his performances in these games (he took 3/25 and 2/26), Cummins was selected for Test squad to play South Africa.

Cummins made his Test debut at the Wanderers ground in Johannesburg in November 2011, in what was only his fourth career first-class match,^[15] becoming Australia's youngest Test cricketer since Ian Craig in 1953.^[16] Cummins took 1/38 and 6/79, becoming the second youngest Test cricketer (behind Enamul Haque Jr) to take six wickets in an innings.^[17] He then scored 13 runs in