A top-order left-handed batsman, Dimuth attended the St. Josephs College in Colombo, which has also given Sri Lanka many legends including, Chaminda Vaas. Karunaratne was very impressive in the domestic circuit as well as at the U-19 level. Looking at his excellent performances at the domestic level, the young southpaw got his maiden international call-up and Dimuth made his ODI debut against England.

He was included in Sri Lanka's Test squad touring South Africa in 2011. Though he did not get to play in any of the matches. Being benched in the next few series, he finally found a place in the playing XI after their leading opener Tillakaratne Dilshan got injured. He made his Test debut against New Zealand on 17th November 2012. He got to open the innings with Paranavitana but had a miserable start to his Test career as he got out on a duck. Though he compensated in the second innings of the match as he scored an unbeaten 60 and took his team to victory. His Test career got a boost after he struck his maiden Test century against New Zealand where he scored a tenacious knock of 152 runs which came from 363 balls.

Dimuth Karunaratne was the member of the 15-man squad for the 2015 World Cup but had a forgetful outing as he broke a bone of his right hand during a practice match and was sent back home. Kusal Perera was announced as his replacement. Since then, Dimuth's prime focus was in the longest format of the game. 2017 was a fruitful year for him as he ended up scoring 1031 runs in Tests and became the second player after Dean Elgar to score more than 1000 Test runs that year. His career-best innings till date has come against Pakistan in a Test match held in Dubai in 2017 where he fell just 4 runs short of his double century. His Test form continued in 2018 where he scored 743 runs in 9 matches at an average of 46.43. His outstanding performances led to his inclusion in the World Test XI by the ICC.

After Sri Lanka's former captain Dinesh Chandimal started facing issues with his consistency and form, he was dropped and Karunaratne was given the responsible job to captain the Sri Lankan side. Under his captaincy, the Lankan Lions defeated the South African team in South Africa in Tests and sealed the series 2-0. Thus, Sri Lanka became the first Asian team to win a Test series in South Africa. In 2019, Dimuth was named the captain of the Sri Lanka team for the upcoming ODI World Cup. Leading a pretty imbalanced team, Dimuth failed to do any magic and the Islanders had a mediocre campaign as they ended at the sixth position in the points table.