In April 2015, Santner was named in the New Zealand limited-overs squad for the tour of England. He made his One Day International debut for New Zealand on 9 June 2015. His first international wicket was when he trapped fellow debutant Sam Billings for 3. During the fourth ODI in the same series he hit 28 runs off Adil Rashid in one over, which is the second highest runs off one over ever posted in England. He made his Twenty20 International debut in the same series on 23 June 2015. On 27 November 2015, Santner debuted in his first Test match against Australia. That match was also the first day/night Test. He also became the first player in history to make his test debut in a Day Night Test Match, where he made his debut against Australia. He hit a boundary off the first ball of his Test career.
2016 World Twenty20
Santner was picked to the New Zealand squad as a premier spin bowler along with Nathan McCullum, who was playing his last international tour. In the first match against host India, Santner won man of the match award for his brilliant bowling performances, which lead his side to win by 47 runs. His bowling performance of 4 for 11 is the best bowling figures by a New Zealand spinner in World Twenty20 as well — .He was named in the 'Team of the Tournament' for the 2016 T20 World Cup by the ICC, Cricinfo and Cricbuzz.
Santner and Jeetan Patel became the first pair of spinners to open the bowling in an ODI in the 4th ODI.
2018
On 16 January, 2018. Santner bowled Pakistani cricketerFakhar Zaman with a carrom ball, something he had been working on for some time, but only recently brought into his international repertoire. In March 2018, Santner was out of the Test series against England, after suffering a knee injury, ruling him out of action for six to nine months. The injury meant Santner's planned spell in English county cricket with Derbyshire and Indian Premier League during 2018 had to be cancelled. In May 2018, he was one of twenty players to be awarded a new contract for the 2018–19 season by New Zealand Cricket.
2019
Santner made the international comeback against Sri Lanka on 11 January, 2019 in the only T20I between the sides before going on to play in four of the five ODIs against India as well as all three T20Is and then two of the three ODIs against Bangladesh later during the same summer. In April 2019, he was named in New Zealand's squad for the 2019 Cricket World Cup. Playing for Chennai Super Kings he hit a 6 from the last ball of the match to defeat the Rajasthan Royals In November 2019, while playing against England at Bay Oval, Santner took his maiden test century. His 261-run partnership with BJ Watling became the highest ever 7th wicket partnership for New Zealand in test cricket. He also took 3 wickets in 2nd innings and became the first New Zealand spinner to take wicket on home soil since March 2018 with 101 consecutive Test wickets in 11 innings in between having all fallen to seamers.