Published: 2020-10-16 18:14:50 BdST
The Knight Riders, coached by former New Zealand captain Brendon McCullum, are fourth on the points table with four wins and three losses and will meet Rohit Sharma-led Mumbai Indians later on Friday in Abu Dhabi.
Wicketkeeper-batsman Karthik has managed to score 108 runs in seven innings this season and informed the team that he wanted to give up the captaincy to focus on getting more runs.
"It takes a lot of courage for someone like him to take a decision such as this. While we were surprised by his decision, we are respectful of his wishes," KKR CEO Venky Mysore said in a statement.
"We are also fortunate that Eoin Morgan, the 2019 World Cup-winning captain, who has been the vice captain, is willing to lead the side going forward."
Morgan, who leads England in the 50-over and Twenty20 formats, was bought by two-time IPL champions KKR in the auctions ahead of the 2020 edition.
This year's eight-team IPL is being held in the United Arab Emirates due to concerns over the COVID-19 pandemic in India.