Heinrich Klaasen is a South African cricketer who plays for the South African national cricket team in limited overs cricket. He was included in the Northerns cricket team for the 2015 Africa T20 Cup. In February 2021, Klaasen captained South Africa for the first time in a T20I match.

In August 2017, Klaasen was named in Nelson Mandela Bay Stars' squad for the first season of the T20 Global League. However, in October 2017, Cricket South Africa initially postponed the tournament until November 2018, with it being cancelled soon after.

On 2 April 2018, Klaasen joined the Indian Premier League side Rajasthan Royals replacing Steve Smith.

In June 2018, Klaasen was named in the squad for the Titans team for the 2018–19 season. In October 2018, he was named in Durban Heat's squad for the first edition of the Mzansi Super League T20 tournament. In December 2018, Klaasen was bought by the Royal Challengers Bangalore in the player auction for the 2019 Indian Premier League. In June 2019, he was selected to play for the Toronto Nationals franchise team in the 2019 Global T20 Canada tournament. In July 2019, he was selected to play for the Glasgow Giants in the inaugural edition of the Euro T20 Slam cricket tournament. However, the following month the tournament was cancelled.

In April 2021, Klaasen was named in Northerns' squad, ahead of the 2021–22 cricket season in South Africa.

He was bought by Sunrisers Hyderabad to play in the 2023 Indian Premier League. In July 2023, Klaassen became the first person in Major League Cricket to score a century playing for the Seattle Orcas against MI New York scoring 110 runs from 44 balls.

In February 2017, Klaasen was named in South Africa's Test squad for their series against New Zealand but did not play.

In February 2018, Klaasen was added to South Africa's One Day International (ODI) squad for their series against India, replacing an injured Quinton de Kock. He made his ODI debut against India on 7 February 2018. He won his first international man of the match award in his second ODI, in the fourth ODI of the home series against India, with a match-winning 43 runs off 27 balls. In the same month, Klaasen was named in the South Africa Twenty20 International (T20I) squad, also for their series against India. He made his T20I debut for South Africa against India on 18 February 2018. On 21 February, Klaasen scored his maiden T20I fifty in the second T20I against India which South Africa won by 6 wickets, he was also awarded the man of the match for his 69 runs from 30 balls, which included 3 fours and 7 sixes.

In February 2018, Klaasen was named in South Africa's Test squad for their series against Australia, but did not play. In August 2019, he was added to South Africa's Test squad for their series against India, replacing the injured Rudi Second. He made his Test debut for South Africa, against India, on 19 October 2019. On 29 February 2020, Klaasen scored his first century in an ODI match, making an unbeaten 123 against Australia.

In January 2021, Klaasen was named to captain the South Africa T20I squad for their away series against Pakistan. In April 2021, Klaasen was again named as South Africa's T20I captain, this time for their home series against Pakistan, after Temba Bavuma was ruled out due to an injury. In September 2021, Klaasen was named in the South Africa squad for the 2021 ICC Men's T20 World Cup.

On 21 March 2023, in a match against West Indies, Klaasen scored his second ODI century in 54 balls. Renowned for his adept power-hitting capabilities, he demonstrates proficiency as a wicketkeeper, coupled with exceptional prowess as a finisher within the contemporary cricketing landscape. His remarkable statistics against slow bowling, where he maintained a striking rate of 191 and achieved an average of 132 against spin during the 2023 IPL, have established him as a coveted asset for T20 franchises.

On 8 January 2024, Klassen announced his retirement from Test cricket, having played only 4 matches since his debut in 2019.